Sounds like worms or parasite of some kind. Might want to take her to the vet for that problem, and just a general health check up. She might need vaccinations also.
Anne with Cats is right - since she was homeless and living outside for who knows how long, she probably does have parasites. She may even have dangerous diseases that she could transmit to you and your family. Here's a link to a website with details on diseases from fleas:
Most of these problems are easily resolved. If you aren't already, you may want to keep her isolated until the vet can check her out. Let us know how the little girl gets on.