Please let go and let this be in the hands of God.
It must be killing you inside to keep involved.
This woman, your child, your blood has a disease called addiction, and she has a mental issue, as well. She has a death wish.
If you have done all that you can to protect her, then you must step aside, and let God do the work of healing or whatever destiny is at play.
This man sounds like a monster. SHe knows this intellectually, but she is clearly sick with abused woman syndrome, addiction, and maybe even stockholm syndrome.
I am sure you have tried everything, but have you considered having her committed? She does not sound well .
Taking money from the grandparents is not a good sign.
Going back to a man who nearly killed her is not a good sign.
I am praying for you to have the strength to release yourself from guilt here, and to release her from your obligation, her from yours. She is no longer present to interact with you authentically.
MAke clear that you support her HEALING and her taking steps to keep herself well and safe. Tell her you cannot keep contact with her unless she takes herself out of his life. This is a boundary.
Men and women, parents, spouses and siblings do this everyday in relation to addicts using drugs or alcohol:
"I will not deal with, speak to, or enable you if you choose to use or put yourself near or use drugs or alcohol, because it will ruin your life, and possibly kill you..."
In this case, you could replace the drugs and alcohol in this sentence with this mans name.
Tell her anything else is out of your reach. Be firm, but loving, and make sure she knows that you support her getting healthy, and being safe, but you will not enable self abuse on any level.
Then, buckle up and take it one day at a time for your own life.
Prayers and support for your heart are going out now. Please be kind to yourself