Not sure if it helps, but for what it's worth, biological kids can do the same.  My DD had a period where DH and I were evil.  We expected too much, we didn't understand her, we (on and on it went).  The truth of the matter was that she was young, insensitive, a smidge ungrateful, and did I mention young.  She grew up a bit, found some perspective, (ditched an unhealthy relationship), and eventually came back to us.  So it's not just SKs who can take all you've poured into them and stomp  on it.  BKs can do it to.  It's not that you're not loved, it's that the pull of others to fill their immature brains can sometimes blind them.

Praying that as she gets older and finds perspective she loses the fog and sees clearly all you did for her.

Hugs!

Return everything you bought her for college, or donate it to a foster kid going off to college that likely doesn't have much. If your DH wants to support her, you two need to separate your finances and he can do it out of his "fun money". If she wants to make the adult decision to cut you all off, then she has to deal with the adult consequences. Don't pay or do anything yourself, and encourage your DH to follow whatever is in his CO.

Sorry she has hurt you in this way - seems many stepmothers go through this.  Do you think her mother is behind any of it?

All you can do is back off and protect yourself. I would not get her gifts, do anything for her,  or reach out to her in anyway.  She may come around as she matures, or she may not.

4 invites is so brutal!!! SS had 10 and it was like playing Russian Roulette. Who get's to go? When you have a close family and grandparents and parents and step parents- 4 invites is just NOT ENOUGH. It is torture. I offered to stay behind for SS's. It made more sense to me that his BM's parents were able to go over me. I wound up going, we snuck like 3 extra people in, but I was willing to sit in the car. 

I know this hurts, I know that you feel betrayed. Just focus on having fun and celebrating at the party after! I am sure there are TONS of parents, grandparents, step parents- from the kids at her school feeling the same thing you are right now. 4 just sucks.

It's a credit to you that you still want to support your SD despite her behaviour. Yours is a complicated case because you also have your DD in the mix who is close to SD. Are they also close in age? If so, what are you/DH going to do in terms of financial support for your daughter? One fast way to breed resentment is for SD to find out that DD got a free ride to college while she missed out.

There is also the question of is it in SD's best interest that you continue to pay regardless of her behaviour. My DH did that for his daughter because he thought she would see that he cared. Two years of college, rent, phone bills and a car later he turned off the tap when he realised he was reinforcing her belief that all he was good for was a wallet. She would ignore all communication until she wanted something and then it was all smiles until she got it. She was becoming quite a toxic user and he was pushing her further down that path. 

So if you are going to spend all this on your SD only do it if you can afford it and with zero expectations in return. That's for your own sanity. If you're going to let DH cut the funding then make sure he explains clearly why there will be a difference in financial support between the two girls in a way that doesn't throw you under the bus. And perhaps leave the door to the college fund open for SD if she changes her behaviour down the track.

I'm sorry I know how badly this sucks. We had custody of Spawn, until she moved out her senior year. She didn't invite any of us to attend her graduation (which was a farce anyway) and then she took to twitter to bash all of us for not showing up. With these kids it's a double edged sword, you are damned if you do and damned if you don't. In my case I just cut Spawn out of my life completely, I realized I didn't need that toxicity in my life. My DH has just started speaking to her again recently and he seems content with the few texts on occasion. I would stop buying stuff, you aren't going to win her affections that way, and just support your DH is whatever he chooses to do. It hurts really bad right now, but eventually it stops and you don't feel so bad.

And stop buying her things. Period.

I was not invited to SD21's graduation, but DH insisted I go, or he would not. Magically a ticket appeared for me.

So, I got to have a decrease in my paycheck for that pp, sit on a hard bench for 4 hours in the hot sum with no hat and no water and certainly not a single "thank you". Dad got a snapshot photo which I did not print and frame, and got her flowers and a stuffed animal and money. SD21 is not in our lives any longer, she moved out and is mooching off Toxic Troll mother.

I would gladly have NOT gone.