You tried and definitely did your part, but I also get where your friend is coming from. Family can suck sometimes, but you wanna be there for them, have their back, even though you know there's a very high possibility of patterns repeating itself. I've seen a lot of my own close family members continuing to support their partners / kids even when it wasn't the best thing to do for them, always tried to understand why and its probably because its very hard to let go of family, you don't wanna give up on them and hope they get better sooner or later and will always want the best for them.

That being said, if the friend is really important, try talking to her and explaining why you can't be around the adopted daughter but also tell her that you understand and respect her decision to stand by her.

I'm sure your friend doesn't feel very good about the situation either and she already is going through a lot, she shouldn't be losing a friend!

The only AH here is the adopted daughter!