Definitely a question for your tax person. You will need to be responsible for some percentage of her cost of living, and as it is that is likely ALL her cost of living. She is, if she is with you for this past year, a dependent, I would think, but do go to professionals for this kind of advice, not the forum. Unless someone is a tax expert here, or has direct knowledge, we may advise wrong and that wouldn't be good.
As far as caring for her being a 'dependent' situation, a quick call to any tax company will answer your question. I think it depends on the length of time the person is living with you--we had a 'foster son' who lived with us for 2 years. I was able to claim him as a dependent b/c we did not charge him rent and he was dependent on us for housing and food.
My link doesn't work because of the period at the end.
Try this instead...
https://www.irs.gov/help/ita/whom-may-i-claim-as-a-dependent
https://www.irs.gov/help/ita/whom-may-i-claim-as-a-dependent.
Going through the IRS list of questions will give you a pretty good idea, but I would still consult a tax attorney.
As far as caring for her being a 'dependent' situation, a quick call to any tax company will answer your question. I think it depends on the length of time the person is living with you--we had a 'foster son' who lived with us for 2 years. I was able to claim him as a dependent b/c we did not charge him rent and he was dependent on us for housing and food.
Good luck--and again, my heart goes out to you.