My SD(16) started using me as the scapegoat at the age of 14, although I'm sure that the BM had been grooming her for years.  My DH would not and has never taken up for me.  In fact, he has done quite the opposite IN FRONT OF HER.  It's hurtful, embarrassing, and disappointing to say the least.  My DH too refuses to talk about any of the issues with SD.  I don't know if he doesn't know how, if he is scared of her, or if this is just how he handles things (i.e., he can't).  But his parents are the same.  I tried for two years to talk so that issues could be resolved.  It would turn into horrible fights between me and DH.  If I tried to talk to SD on the few occasions I had the opportunity, she would just start crying and not particpate in a conversation (she has done since I met her at the age of 7).

I haven't had to endure the social media shaming.  She took too much pleasure in blocking me and everyone associated with me from facebook.  She asked to be my fb friend again eventually and I accepted only because I felt like I had to, less i be even more evil than already portrayed.  She has asked three people who she deleted along with me.  My sister and two friends.  None of whom accepted.  And I realized why this made me so happy.  FINALLY, I felt like someone was sticking up for me to her.  Because nobody in my family would.  Not my DH, not my in laws, and not my SS.  Not that I think it's SS job, but he could have said, "Hey that's insane.  I know you have not been mean to her."  Silence.

I have completely disengaged.  Completely.  It is the only way to cope and for me to have somewhat of a happy life.  My DH claims he loves me so much and he loves me more than anyone in the world.  He just doesn't act like.  SD rules the entire family.  They gave her all the control.  I'm the only one who would not bow down to her and I have no intention of doing it.  I apologized to her (not sure for what) more than once.  I have tried to talk to her.  I have tried to have a relationship.  All of which I did for my DH.  I knew it wouldn't help but I had to show all of them that I tried and take myself out of the equation.  If I don't do anything and am not around, i cannot be blamed (or shouldn't be).  She doesn't seem to get it's a two way street.  Entitled, manipulative, teenager, with a mother who taught her everything.  It's the perfect storm.

People with BPD can be extremely challenging to deal with, especially if they are not actively seeking treatment. 

The BM in my case has not been diagnosed, but three counselors I've seen and the couples conselor DH saw with BM during their divorce flagged her "borderline tendencies". She tells terrible lies about DH and me and DH's family believes her. 

It's extremely exhausting, frustrating, and disheartening. I've worked with several counselors to figure out how to deal with that. All of them have told me that my reactions are normal, but there's not much I can do to make her go away. They have advised that I should avoid her at all costs. 

It has been extremely hurtful that DH's family believes BM and thinks she is only looking out for the best interests of the children. Even when I've shared some of the specific incidences and even though they've been copied on emails where she's made claims that are obviously lies, they still see her as  "a good person" and have accused DH of just "being at war" with her. I think that's the hardest thing to deal with, the people who believe the lies.

You have to suffer in silence and that feels so unfair. Thanks to my mother, my mantra has become, "you what the truth is and that is enough." If others can't see the truth, I have to move to a place where I don't care what they think. That is *hard* very, very hard. 

I recommend that you find a good counselor. One who is familiar with the trauma that being the target of blame for someone with BPD can cause. You might want to find a couple's counselor who can also help your DH understand the role he needs to play. When DH and I saw a couple's counselor together and she was clear with DH that he needed to set clear boundaries with BM. This was before we were married and if I'm being honest, the counselor told me that I should really think twice about marrying DH because "her behavior will not get better, it will only get worse." She was right, but I don't regret marrying DH. He has gotten much better about maintaining boundaries with BM, which has caused him a lot of grief and created a wedge with his family. My biggest concern is that one of my SSs will also develop "borderline tendencies" or BPD, like your SD and then DH will be the target of blame for him. 

I wish you the best. This has been the most challenging, exhausting, and frustrating experience in my life. It's been so disheartening to see how DH's family react and involve themselves. I feel heartbroken for DH that his family is so unsupportive toward him. 

Disengage completely and focus on you and DD15. Let DH pursue the relationship with SD. I found at least in my situation I have protected SO from much of SDs behavior by dealing with the brunt of it myself and ultimately becoming enemy #1 as a result.  As I have stepped out of the situation,  he is starting to see things on his own. That being said, it will be some time before he even gets close to seeing her for who she really is, as he has not yet been the one in the position to be used and abused by SD.  In the beginning we both thought it was a good idea I interact more with SD as she was just beginning to experience puberty and he felt she would benefit from having a good relationship with me so she could have someone to talk to.  I truly made every effort to have some kind of relationship with her and at first I thought I did. But over time it became clear she never liked me or respected me. She only cared about what what I could get her or do for her.  She never appreciated a single thing I have ever done for her. She is the same way with BM and SO.  She can bully BM I to giving her what she wants or giving her, her way.  The only time I have ever seen SD be nice to SO is when she is about to ask for something.  The only time I have ever seen her show him any affection or say she loves him is after he has bought her something.  As for me SD has basically said she no longer has any use for me after I put my foot down and told her I was cutting her off and if she wants or needs anything to ask her parents. 

SO is basically in the beginning of going through all the motions I have already gone through in trying to have a relationship with SD. I make it a point to not give my opinion or personal experience and just support him in his efforts.  It's hard for me to sit back and watch as he gets his feelings hurt by SD but I dont have any other choice, he has to figure it out for himself. 

I'm so sorry you're caught up in this mess caused by someone else's baggage. It's clear you are a compassionate and loving person, and unfortunately you and your daughter are in the path of a BPD hurricane.

You have options, and you have rights. You have the right to a peaceful existence, and to be treated with dignity and respect.

It sounds as if your H doesn't know what to do. He's frustrated and feels helpless, but that is not an excuse to treat you poorly, and being married doesn't mean you have to accept poor treatment from his daughter or him.

I can well remember going though a similar time when BPD YSD lived with us. I was an emotional wreck, and felt very conflicted. I didn't know how to draw boundaries or create some safe space for myself within all the chaos. And even after YSD ran off, it took a good while for me to calm and feel safe again.

I think it would be helpful for you to create a list of your priorities. This can help you focus more on you, and less on the chaos caused by your H's mentally ill baggage. Clearly defining what your role is and isn't may also help give you emotional distance from his daughter, which I think you really need. Obviously you own daughter's well-being should be job one, self care, your career, etc. Define what's important to you right now, and try to just stick to those things.

 Detaching emotionally from this hostile, unpredictable, mentally ill person is essential. You can't fix this, you can't control this, and you don't have to offer yourself and your daughter up as collateral damage. Let her go. Accept that she is a danger to the well-being of you and your daughter , and focus on giving your daughter a safe, stable adolescence.

She doesnt get the furniture. Not a stick of furnishings will be given over to her.

Because shes "ill" doesnt excuse her behavior and treatment of you, the abusing and harrassment as well as the slander on social media. She is not "deserving" simply because she shares DNA with your DH. That would be a no go zone.