How can my mother-in-law become our dependent and get put on our health insurance?

Is there any way that my mother-in-law can quit working right now and move in with us and become our dependent and therefore be put on our health insurance, etc...She currently has I think between 6 months to 1.5 years left before she can retire, but she makes only $18k/year, so she might as well not be working. She has tremendous arthritis and really shouldn't be working. She works "part-time", but is made to work full time hours. Go figure. Anyone know the answer to this?
--------------------
It really depends on the policies of your health insurer if you could add a parent, so you should call them. She should consider looking into getting disability from the social security office (1-800-772-1213). Also, if she has little money, she may also qualify for Medicaid.
Source