I have been at this longer than you. It isn't easy. We bought Kay a house, a mobile home, put down money for rent when she lost her homes, bought her cars...think of it, we did it. We even had a fully paid college fund but she hated school. We would have paid for any therapy but she would not go.
We have a very small retirement fund now. My other two resent her and every leg up we gave her was a bust. It didn't help her get on her feet. Instead she demanded more. That is all it did.
We are not close like I am with the other kids and nieces and nephews. No hugs. No love. Just abuse over what we should do for her.
We are done and it still hurts, but we see now that nothing will change her unless SHE wants to change. Not expecting her to change any time soon. She is full of anger and false memories of her childhood "abuse" that never happened. We never even spanked her and she got more attention than my other two combined. We really tried.
Her life is now pot.
I think it is important for us to think of ourselves first, even if we are not yet ready to stop trying to change our kids.
Be well.