This happened to my mother while I was still home and in college. Her best friend was also in a crisis situtation and she and her 2 daughters (a 2 yr old and a 16 year-old) came to stay with us during Christmas after they got kicked out of their rental.
We too went through all of our food, wound up spending tons on presents for her kids, and chaufering them into town when they needed rides. They were only supposed to stay a week (during which time they were supposed to secure a new apartment) but wound up staying for a month and a half and not even trying to find a new place to live.
Needless to say it was a horrible experience for us. But we didn't want to "kick them out" either. In retrospect we realized they took terrible advantage of us. It finally came down to my parents packing her things for her, and my dad finding a landlord willing to let her move in the same day. While she was in bed sleeping in and her older daughter was out with a boyfriend, my dad packed her stuff in his car, and calmly asked her to hop in. He dropped her off at the new rental and said "Glad we could help. Hope you like your new home" and that was it. End of story...no thanks etc. In fact she was mad at us and for about two years kept trying to find ways to get us to "help her out of jams".
Be glad she left. You wouldn't want this to be the start of an unhealthy relationship of codependance and headaches. If my parents didn't get spine when they did they'd probably still be taking care of this woman and her two daughters!