The thing about this kind of disorder is that the person can be very nice and appears to function normally but is not. There are also 2 kinds of bi-polar disorders. Knowing the difference and knowing which one she is will also be helpful. The thing is, no matter what you do, she will not truly feel empathy towards you even if she appears to care. I had to get that in my head. I have been seeing a psychologist about this matter. I'm going through something similar with my sister and the only way I can keep myself sane and for my child to be emotionally safe, is to avoid her. I mean, there are days when she is SO mean that I doubt my own sanity. I have spent too many days wasting my time trying to accommodate to her, neglecting my child and husband in the process.
Take care of yourself and your family first, and don't feel guilty about it. If you get sick or too hurt from caring for her, she won't have you anyway.
Oh, I also found 2 supportive websites recently:
The second one is for spouses of chronically ill people but I found it helpful because, well, a sister is as close as a spouse and I found some of the stories there inspiring. Both you have to register for, like Mamasource. They might have more insight on caring for a home bound person as well.