Hi, Hon. Look, you are an adult and know about Life with Daughter more than anyone else, including your parents. Be respectful to your parents, but you are a mother now and do not and can not always do things that are bad for you to please them. They are crossing a boundary by telling you what you should do about your adult child who isn't benefiting by living with you. In fact, she is refusing to help herself and I'm guessing she is abusing you.
Unfortunately, difficult adult children can cause differences of opinion in some families, but as adults ourselves, I feel we need to continue what is best for us. It's possible one day dad and mom may offer her a place to stay. Let them. This is their decision. It's not like you didn't warn them. Usually the Grands end up making them leave too, with new respect for what we dealt with. In other words, we have no choice when making difficult decisions that others may disagree with, out of naivety, we take a risk that other people could become righteously mad at us.
in my opinion we need to be strong and develop thick skin, even with family. When other opinions stop is from doing what is best for us and our difficult adult kids, we lose our adulthood and power. We need to do what is right, not what pleases our extended family. They are not the parent. It is good to show your daughter and other kids that you are your own adult person.
Tell MOm, "I agree to disagree but prefer not discussing this issue."
Mom: well. I didn't raise you to throw out your daughter...
You: oh, I hear the door. I have to go now. Love you!"
You can try to explain, but you probably already have.
The definition of insanity is doing the same thing over and over again and expecting different results.
Have a peaceful day focused on YOU for a change.