BettyAnn - this is SUCH a hard situation. I do not envy you at all. It is so hard to "evict" anyone - never mind a friend. But like you said, there is a point where charity crosses into being abused.
It is something we were talking about in other threads, in relation to many current best-selling books - Eat Pray Love, and Three Cups of Tea. In both cases a nice person offered charity and the recipient began taking advantage of it.
As the "giver" you have a responsibility to yourself - and to others who depend on you - to draw the line. You can't let yourself be drained dry. I know it's really hard. You shouldn't be in this position. But as the books say, you have to deal with the situation you're in. You need to be gentle but firm. You have done your best to help, but you cannot allow your own world to be destroyed. There are MANY other organizations out there whose purpose in life is to help out. They need to start taking charge of their lives and hook up with one of those organizations. You do not have the money or training to help her on with her next stage.
Your health is really being affected by this. You shouldn't try to "grin and bear it". Only you will speak up for yourself. She DOES have other options. It is time she take the responsibility to go after them. Give a reasonable deadline, but then hold firm to it. Help her move - but she MUST move.