I'm inclined to agree with volunteering. You have an education, so it shows that you are definitely trying. But the economy is rough at the moment. Even my mother - with many years of experience behind her - has been struggling for work. Volunteering could give you experience, at the very least.

Your sister sounds like a horrible person. I wish I could offer more advice on how to get out of there. But I struggle financially myself because of my mental illness, so I don't often know how to get out of such a situation.