It would depend on where abouts you live on what would be available in your area. Is she seeing anyone about her mental illness? Therapists I assume would have information on local housing options. Also any local charities would be a good place to start. They don't all provide accomodation options but may know of others who do and may be able to point you in the right direction.

Also, it might be worth doing a google search to see if your area has any local mental health services. They would also be a good starting point, especially if she may have special needs or be unable to live alone.