I think she's cute! But you won't be able to guess (or at least have a good guess) until she's older. She looks like she could be all of the breeds you mentioned-minus the boston-to me.
Her poor belly! In the second to last photo, is that a hip bone I see? As in, if she didn't have worms she'd be pretty thin? Poor girl, she can't be comfortable with a belly like that. I'm glad she's found a home and getting treatment. Can't wait to see her grow up!