On the FAFSA, you only have to report one parent if yours are divorced and you are claimed as a dependent. However, if you are independent (ie you live on your own, pay your own rent, etc), you don't have to report either parent on your FAFSA and that will allow you to borrow up to the cost of attendence. Your mom's income is so low that your estimated financial contribution from her will probably be 0, so you should list yourself as a dependent to her, assuming you actually live with her and aren't intending to defraud the federal government. Also, your parents probably rotate who gets to claim you on their tax forms, so you have to go along with that if one of them claimed you this year.
http://www.finaid.org/questions/divorce.phtml
My school required additional forms where I had to report everything (both parents' incomes, professions, siblings, etc) for institutional aid/need-based scholarships, which I actually got a tiny amount of (being near the low end of the socioeconomic scale for med school).