Welcome Willpower,
I am so sorry for what you are going through.
You are an adult and have to make choices that are best for you. I commend you for making such a difficult choice.
You could tell your parents something like:
You: While I appreciate your concern I would ask that you respect our decision.
Parents: We can't it's cruel what you are doing.
You: What's cruel is the way she is treating us. She has no respect for our rules or boundaries. We have tried to help her but our helping is no longer helping. She needs more than we can provide.
Parents: It sounds like you are giving up.
You: We will never give up but we recognize our limits and we have reached them. We have made our decision. We will just have to agree to disagree.
Good luck!
Let us know how it goes.
