My daughter was exactly the same, totally interchangeable with yours Morethan2.
She divorced the father of my 2 GDs 10yrs ago and took up with a physically abusive, drink and drug abuser. Didn't work, lived on benefits. From her late teens we had supported her both emotionally and financially through eating disorders, her first marriage and her abusive relationship. Always being asked for money, always gave it, we could not see our GCs suffer. We went through court cases with her for custody of her child with the abuser, despite it being embarrassing for us, and she kept him by the skin of her teeth.
We took our GDs away from her eight years ago after repeated fights between them and police interventions, and they have lived with us ever since, their mum and dad see them regularly and they are fabulous girls. Eventually she threw out the partner. Then one day, about 5 years ago, while still supporting her in every way including daily money for nappies, food, electricity etc, lending her my car, paying £100s to her to look after her own daughters while we had a week away from it all. One day I refused to lend her my car as I needed it myself, she was verbally abusive, told us we'd never helped or supported her, and we wouldn't see her son again.
I can't describe my anger, it was overwhelming, as if we'd been conned all those years which, of course we had. She always took, never gave back, not even a thank you or a bunch of flowers ever. With hindsight we should have stepped back all those those years ago and let her get on with it. Well we stopped contact with her immediately and it was absolutely the best thing we'd ever done. Eventually slept through the night for first time in years, worries fell away from us and DH and I finally led a normal life together.
Of course she survived, made new friends and manages ok on benefits I believe. Hope you find some inspiration in this Morethan2