Read up on this website for proof - you do not want to marry into this nightmare. It will not get better. Nothing you do or say can change this. Please spare yourself a life of misery and abuse & just get out. Your fiance had 100% failed to nip this in the bud - please don't smoke the hopium "Things will get better after the wedding" pipe. 

Your blog had zero reference to your fiance correcting his spawn, so I assume she runs the show and he makes excuses for her rather than man up & not tolerate his fiance being treated like b.s. Keep in mind this is his pre-marital "Honeymoon " level of effort. Just wait until you're legally locked in and he can blame you for causing his little drama-queen to act this way!

Knowing what I know now about this stuff, my truest advice is to RUN LIKE THE WIND. But don't take my word for it - read up here on the past 20+ years of blogs on this website. 

How does your fiancé deal with these theatrics? My husband would have looked at his daughters like they had three heads if they cried for him to put them to bed at that age. The ONLY way this is going to turn out well for you is if your guy is behind you 100%. He needs to shut this shit down now. Thirteen year old girls are a special kind of hell under normal circumstances and this kid sounds like she's running the show. Please think long and carefully about this before making your relationship official. Best of luck.

Resolution is highly unlikely. Ever.  Make sure that daddy is ready to marginalize his own failed family spawn when she never stops the crap.  His priority is you and him, and your relationship. She is the top adult responsibility... until she turns 18 at which point she becomes entirely irrelevant unless she learns to be respectful of you, her dad, and your adult relationship.. .and she behaves reasonably.  Which pretty much... ain't gonna happen.

The odds of success from th starting point you describe are.. slim and none. At best.

In situations like this a Sparent has to lower their expectations so they won't be disappointed. Not somethign I would have tolerated in my blended family relationship.  I was all in and all I would accept was a life of adventure and a love for the ages. 

SS has been a big part of that, though we started long before the shit storm your SD is perpetrating. SS-31 was 15mos old when we met. We married the week before he turned 2yo. DW was the CP with full physical and legal custody and the SpermDad had limited long distance visitation starting when SS was 2yo.

I'm dad, our home was his home, and we, the 3 of us, are his family.

My experience is pretty much the Unicorn of SParent adventures. My DW is the Unicorn bioparent to partner with, and our kid is a rare SKid who recognized that being a decent person was far more pleasant than being toxic failed family crotch goblin.

Set your standards of behavior and standards of peformance for your mate and his spawn. Tolerate zero deviations from those stnadards. If you don't, embrace the misery because it will happen.

He has had 5 years to fix it and for 5yrs he has failed to fix it. Odds are he will continue to fail at fixing it.  IMHO your only shot at any relationship joy will be to purge her from your home and demand that daddy has his toxic kid have their time together away from you and your relationship though only when you do not have demands on the marriage.  They fit them in when you say they fit them in. Which he will in all liklihood refuse to do.

I wish there was a notable probability of success for your happiness in this relationship.

Take care of you.

That situation did not change here until DH and I began truly handling it. But it was hell before then and has not been a walk in the park. 18 years in, and SD and I do not communicate. 

When SD, then in middle school, learned that Daddy was dating again 5 years after the divorce, she threw a fit (and threw the phone across the room). When we'd see her, she would squeeze herself in between us, grab DH's hand, clearly trying to push me out of the way. DH would very gently correct her. He had to constantly tell her to tell me "thank you" whenever I gave her something, cooked for her, etc. (she would look at him and thank him). She was often very inappropriately climbing onto his lap, hugging him, being extremely needy and clingy. She would do this "baby shuffle" walk and baby talk. During this time, I was very supportive (and actually pushed) of DH spending alone time with the Pwecious. DH was the guilt-ridden Disney Dad who felt sorry for his Pwecious Pwincess.  

SD came to our wedding. I took her to the nail salon with me and we had manis and pedis together. I wish she had just stayed home. Most of our wedding pictures have her in them with this purposely forelorn look on her face. It is disgusting. I have never hung those photos in our home. I was told that after the reception was over, SD broke down screaming and crying. She was well into her teen years then. 

You mention that this should be a happy time in your life. I did not experience "a honeymoon period" with my husband because for the first two years of our marriage, all hell broke loose. Within 4 months, SD stopped speaking to us (to punish us/him). That lasted two years. She wrote horribly hurtful letters to her father--one suspiciously arriving on our first anniversary. BM was clearly in on this/guiding this and she began harassing us. I kept saying to DH, "This is supposed to be a happy time for us. Why are they trying to destroy it?"  Because SD felt like I was not only replacing her mother, but also her. Stupidly, I dug in my heels and was not going to let them win. At the two year mark, I was ready to throw in the towel. That's when things began to change. 

Ultimately, SD's fear was a self-fulfilling prophecy, as she is barely in our lives. I have seen her three times in 13 years, and just a handful of times before then. When she began speaking to DH again (because she needed money), he asked me what I thought of him taking her on a trip he had planned to a resort area for business in order for them to reconcile/reconnect. I said no...she hasn't earned that. So she was not invited. She has missed out in ways she cannot possibly imagine. BM has been totally out of the picture since 2009. We saw them at a wedding. 

We got through it, but I would not wish those first years on anyone. The feelings do not go away (SD was in therapy and--this is a big laugh--is a therapist herself). She still resents me and practices passive aggressiveness toward me (usually during the holidays). DH goes to her (out of state) if he wants to see her. There is/was no logic to any of it. Our therapist said, "You cannot place logic on the illogical."  It was all a toxic way of dealing with life fed by the BM.

*Of course, there were hints of dysfunction and weirdness before we got married, hints that I purposely ignored. I understand how difficult it would have been/would be to call things off, to leave a relationship where you've invested so much. We have made it through. Skids are in their 30s. And even though they are far away, there are still issues (thus me being here), but nothing like the earlier ones. My suggestion, like others, would be for you to do the difficult thing and get away from this situation unless your SO steps up. Without basically removing his daughter from the equation (unless her behavior magically changes), the pain and anguish (abuse)--be it for months, a few years, or, God forbid, decades--is not worth it.  

Don't do it. SD14 showed signs of mini-wife syndrome when DH and I first started dating (she was 5). She only got worse as time went on. We no longer have a relationship. Her parents had been divorced for YEARS, but I was still the bad guy in her eyes. There was definitely PAS going on, but SD14 also has her own set of mental health issues. 

She cried at our wedding and pouted the ENTIRE time. Downplaying it later saying they were "happy tears". We got ZERO good pictures of her. 

She cried when we told her we were having an ours baby. Said she decided she didn't want a sibling anymore.

DH spoiled her rotten when she was young and she literally could not comprehend when someone else other than her came into the picture. She didn't understand the difference between children and adult relationships. 

DH no longer enables the mini-wife and sees more clearly now. SD14 100% perfers BM and I will always be the bad guy just for existing. Like I said, we no longer have a relationship. I don't want one. And definitely won't encourage her to have one with our son as well. DH knows she is a carbon copy of her mother, but of course still have a responsibilty for her until 18. 

Don't do it! The only way my situation got "better" is because I disengaged. But it's not ideal. 

You must be ready to disengage from her.   You must become the evel SM.   DO you really want that life?  Remember you can not do more then the bio parents.  

Your SO put his daughter on the same level as him and he cannot un-ring that bell now.  Your SO has treated his daughter like a peer and equal and there is nothing you can do that will change that dynamic.  Many of these divorced fathers turn to their daughters to “take care of them” now that they no longer have the BM there taking care of them.  The daughters love the attention and feel special because “daddy needs me so much”.  It’s a completely unhealthy dynamic created by a person (your SO) who obviously does not understand healthy relationships.  It’s not like he did this with malicious intent or for a sexual purpose, but he has created this toxic unhealthy dynamic and unless he is willing to see that, acknowledge his part in it, and take the steps to correct it, this will not change and will only get worse over time.  Women do this as well when they make their sons “the man of the house” once the father has left. 

I don't have any additional advice than the ones already here. Seems that having an SD comes with even stronger feelings of jealousy and possessiveness than having an SS? But there is still that with my SS. I remember once overhearing him tell his friends while playing online video games that he was a "daddy's boy" and was waiting for his friends to chime in in agreement or something. I think he got ribbed instead because SS never repeated that. I think he wanted a mini-wife vibe with dh, but couldn't get away with it as well being a boy.

Interestingly, SS did not fuss or cry at our wedding, and smiled big for the camera. He actually loved seeing old family friends and family. I do know that he was talking badly about me to at least some of the people (because it was mentioned to me the next day). I sometimes wish he would be open about his feelings about me and my relationship with dh. Instead, SS has become quite slick, and gets in digs only when he think he can get away with it in subversive ways. I wish he was more open about it so that I could point to behaviors as "evidence". As it is, I just feel gaslit a lot of the time.

You don't have an SD problem: you have an SO problem. I didn't see anything in your post about what your SO is doing to help his DD get over whatever issues she has. The reason is because Mini-Wife Syndrome gets enabled by the dad because of his own deep unhealed issue. Ask me how I know. 

I could write an epic response about my own mini-wife on steroids34 but I won't. It's been awful. I'm still with my DH because we've been together 28 years and have built a life but it's been nothing less than soul-destroying for me. Three years ago, I was about to leave but my DH finally went to individual therapy, I went and then we went to marital therapy as well. It's been a long haul because we both were very broken people and had horrific childhoods so we had a lot of work to do. Healthy people don't foster Mini-Wife Syndrome. My SD has actually improved quite a bit although I sill hate her fucking guts and she still has major issues. Also, my DH puts up a lot of boundaries and no longer falls for her shit. He is well aware that if he slips back into the mini-wife dynamic I'm gone and DH's currency is that he's quite proud of having a long-term marriage and he doesn't want to ruin it. 

Don't make the mistake of counting down to 18. Mini-wives don't meet milestones when their peers do. In fact, they create a dependency to make it so that they stay with Da-da forever. They also get sneakier and ramp up their tactics. Also, don't fall for your SO's gaslighting, "it's just a stage," "she's a teenager and teenagers are..." "she just needs to adjust," and so on. I even got, "well, you didn't have a healthy relationshp with your father, so ou don't understand." I also got, "well, you don't have kids, so you don't understand." That was before we had our DD24 together. 

The prognosis for Mini-Wife Syndrome is slim to none. I realize I'm in a very rare situation where my DH actually wanted to change. Most of these dads don't. They're perfectly happy with their situations so they don't want to change. They'll maybe make fleeting changes because they don't want to lose thier SO but if they truly don't believe there's anything wrong with what they're doing, they won't change. That, or they have a fear that is greater than their desire to heal. My DH had an intense fear of losing my SD, so whenever there was any sign of healing/evolvement, he'd do something to knock everything back into status quo. He had his own unhealed issue which is what fans the flames of the mini-wife dynamic. They feel that it's the SM's job to just come along for the ride and if she says anything she gets accused of not supporting the father/daughter relationship. How dare she expect to have a "real" marriage and be treated like an adult. How dare she want to have a say in her own relationship or household. There is such a thing as supporting the father/daughter dynamic but you should not have to enable a dynamic that hurts you.

I suggest you do not marry this guy. Tell him that you're putting the engagement on hold until you see at least a full year of intesnse effort on your SO's part to take charge of his family and put a stop to the mini-wife dynamic. Maybe get him to a therapist for couple's counselling. Make sure YOU interview therapists before you choose and that they have education and training in step-families because so often therapists don't have that and will put all the blame on the SM and cause more damage. 

I've been in the game for 28 years and I developed physical symptoms from coming a distant last place to a mini-wife for so long that my doctor and I thought I was going to die. Please don't do this to yourself.  

My husband's kids were adults (chronologically) when we met and eventually married. I didn't have words for it then, but I had a major miniwife situation.

She cried when we got engaged. She was sure he didn't really love me. She would take care of him when he's old. DH and SD acted like a couple when together and I was the third wheel or just ignored.

After several meltdowns and good counselors, DH realized that I was his wife all the time and he couldn't set me on a shelf when he wanted to cater to SD. DH did the hard work of changing the dynamic, and I am finally his only wife.  SD though no longer speaks to him, over some real or imaginary thing DH said or did several years ago.  She won't even tell him what she's mad about (because it's an excuse) so he has no way to address it like an adult. 

My story is not unusual here on Steptalk. Use it as a crystal ball for what lies ahead for you.

Does your SO actually lay down in bed with his 13 year old daughter to help get her to sleep?

A 13 year old who has had a negative view of your relationship and been openly expressing it for a few years is highly unlikely to change her mind until she is well into adulthood and able to separate herself from her father and see him as an individual with individual needs. Even then, experience from those on this website tells us that many of this children of divorce hang onto their anger and sense of rejection far longer. 

1. These divorced parents only care about themselves and their kids. It is all about what you can do for them and their kids. 

2. More often than not their kids are nothing special. In fact most of them are spoiled brats who end up amounting to nothing in life.

3. They do not care about you on the same level. 

4. If you end up marrying him knowing this you have only yourself to blame for your miserable future.

5.They are users.

Read up and research mini-wife syndrome. Youve got a mini-wife.

Id not marry into this, knowing what I know and reading others stories over time. It doesnt get better it gets worse.

You know this, because you are here asking.,  against popular thinking.  [ I tack family's BM'S]. SD is not on equal level as you.  SD is a child, and she does what she is told.  
Your problem is your SO did not shout her down and put her in her place.  First of all, when she pulled that crap on vacation. SD would be punished to her room.  Then punishment when you were home.   SD Should be told go live with her mother. GM. or anyone who would take her.  
'Do not get married,  time for a period of time where you and SO break up.