If you're desperate for suggestions, here's one. Do you have connections to help her find a new place to live? Many times people are so busy working, or just trying to keep their head above water, they don't know how to go about finding a new place to live. I know it's not your fault, and you've certainly given her enough time, but if you could solicit a place for her to move to, she might happily leave.
You could try an ad in Craig's list. Doesn't cost anything and you can have section 8 landlords call you. "Please help, desperate for housing".