This is a complicated situation, my prayers are with you. I have a family member struggling with some issues with her daughter, she has been thinking of relinquishing the parenting rights and have the state take care of her daughter. She needs to do it but has not wanted to do so because she fears the outcome and once it's done she can't take it back. Her daughter is 20/21 years old and her situation although different from yours is as well very damaging to all involved. It comes to having her daughter end up in jail or giving her to the state because she can't take care of her.
Of course as a mother she has not been able to come to terms with letting her daughter go but in the other hand the on going pain and costs of her daughters actions have become such burden is taking a toll on everyone.
To her and as well to you, I can't find words of advice to help other than y'all be on my prayers for I know the love one has for our children can bare it all.