I don't know how you stop feeling guilty, but you are doing the best you can in impossible circumstances. You can't fix her life, no matter how much you (or your relatives) try, unless she's willing to take steps to resolve her issues herself.

If you bought her a home, you wouldn't be able to control what she did with it. It could be gone in a year or two, when she sells it for her next big move. I'm really sorry you are stuck with this situation. No contact sounds like a very healthy choice.