Treat them the same way they treat you. That only fair.  Your DH has to paid his share of the house hold bills. So very little money is left over for SK.  

Do not "work your butt off" so that DH has money to give his offspring.   I have never contributed towards the SDs financially and wouldn't even consider it.  Besides, at the age of 25, it is ridiculous he is still financing her.  If she wants to continue getting educated she should get student loans.  

I didn't go to my SD24's graduation.  I had no desire to be in the company of NPD BM and all that family all day. 

Turns out you can’t buy love or respect. Stop funding these adults. If DH wants to, he can work his butt off. 

While he is away (or before) read "Women who love too much".  

Treat the SDs as though they were mere acquaintances.  And just like acquaintances, that does not include giving them financial (or other) help.  If your DH does not agree with this, separate your finances, get your own will, and plan for a future which is mostly uncertain with one exception - these girls have never accepted you, won't accept you and will only include you when it is to their advantage.  And then they will then dismiss you as insignificant, once again.

If your DH wants to see them, attend their functions, etc. then let him.  You don't have to go.  Find excuses or ways to get out of it.  That's how you start disengaging.  The graduation is just the first step.   Don't make any big announcements, just tell your DH, "I fully support you going to SD's graduation.  I hope it is a great event and you have a good time.  But you will be going alone, since I won't be going and have made other plans."   And indeed, make other plans.  Visit a relative, go do volunteer work, whatever.  

I can tell you that I put in almost as much time as you being in my SD's life.  And like you, I was treated (at best) with insignificance and cold politeness.  It was also terrible to watch the heartache SD inflicted upon her father and his extended family.  Just one example - she couldn't even be bothered to call her grandmother when her grandfather died.  Nor did she attend funeral or even send a card or flowers.  I decided this is a person I would never have anything to do with if I could help it.  I did the best that I could for as long as I could but then I let go.  

My only warning is that just when you think you've found peace with disengaging, something else will come along that tries to suck you back into stephell.  Even when they are adults.  

It never ends.  

Learn to disengage, which includes mentally pushing them out of your thoughts as best you can for as much as you can.  It's not easy but IMO it's the only answer.   

Disengagement will set you free from this treatment.  2Tired4Drama gives good advice.

Stay here for support.  I could have never accomplished my disengagement without Steptalk and the advice here.

It is very difficult.   Be discreet,  have patience, know this might take years after this length of dysfunction.   

I have given myself the best gift ever,  after 30 years of trust went away in one day.  

I will never go back.  It took 8 years for me to be free.

Hugs!

Most of us on this site got sucked into the picture of 'blended family bliss' when we first got married.  We wanted to succeed and held on for years, donating to skids education and support while being treated like we were invisible or worse.  As many have suggested, disengage.  Don't give them another dime of your money, minute of your time or a smidgen of your thoughts.

Just wondering why YOU were working your butt off rather than your DH?

Why are you still involved?  If the other girl is decent to you then have a relationship with her.  But if the youngest one is not then be done.  Look, I get it.  When they were young we were essentially obligated.  And there was a transition from kid to adult.  But they are well past the age where they are equally responsible for any relationship you do or do not have with them.  They may be related to your husband but they are people like anyone else.  You don't get along and she did not invite you to her graduation.  So what?  Let her father go to it and you do something fun by yourself. 

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 I texted her taking up for her father and told her to be more grateful. 

This was your mistake, DH should be fighting his own battles with his offspring. If he wants gratitude he needs to ask for it, not you demanding it for him.  What you said was true, but it was not your truth to tell. It never bodes well for SM to jump in and try to rescue DH from the first family drama that he created.  You've been the flying monkey trying to smoothe things over for DH and he has happily allowed it because it gets him off the hook.  

Time to listen to the disengaging advice above and step waaayyyy back. 

There are many women here who would disengage and be okay with no invite. I would have no respect for a man who couldn't/woundn't stand up for me and our relationship. It is not accptable to try to split a married couple which is essentially what SD is trying to do. "pick me Daddy, Pick me Daddy." Can you imagine if DH treated her SO this way?

Do what is best for you and what you can live with. Best of luck 

It’s been more than proven that college is NOT a necessity in life to be successful so why are you paying for another grown adult to go? I know you think you’re helping but actually making her take out loans in her own name and working to make ends meet is a big part of maturing and growing up into a self sufficient adult. You are just as bad as him for enabling her with that but I digress as that’s not what your post is about...

anywho...I think you asked for it when you texted her telling her to be more grateful. You can not control how someone treats another person. If her dad doesn’t stand up for himself she will always treat him as an atm. HE needed to put a stop to it. By you stepping in, you gave her a target on your back. Now she can cause conflict and work up to play the victim card to daddddyyyyy about mean ole stepmom who never loved her anyway **eyeroll** This is one of those things that required tact. But wants done is done and now she’s waging war in your household. So you cut her off. Directly and indirectly (giving dad money to give to her or buy her things). Encourage him to go to her graduation without you. They’re long and boring anyway. He should be there as it’s his kid and nothing will ever change that. If you make him choose you are providing her again with another victim card. Stop playing the game and she’ll get bored and get over it. Tell him to go and have a good time (don’t remind him to pick up flowers, let him fail a little so she can see WHOs been doing the work these last few years) and go enjoy a girls night out with friends or go hit up a movie. Post about it if your feeling petty and then when he gets home ask him about it if you actually care. Chances are he’ll say it was “good” “long” “couldn’t find her after” “forgot xxx” whatever and it’ll be done with. It’s hard to let go when you’ve invested so much into a relationship but in this case you need to walk away from the toxicity.