Ann, it looks like you have a diamond in the 'ruff'. I'd say she lucked out in finding you.
The wounds on her head looks more like deep scratches, like from a fence, than from fighting. Her belly pic shows she definitely had a recent litter but most likely not currently nursing. Did you try to express some milk? That might be telling as to whether she still has nursing pups somewhere.
My youngest son has 2 pits (well, one is a mix) and they are both real sweeties. He also has a small poodle and 2 mini-dachshund, chi mixes and all the dogs get along very well.
We had Christmas dinner over there yesterday and there were some puppies there that some of his in-laws had. The pits had never seen these dogs before but were very tolerant of them. One of the pups was very small and Sadie, my son's pit girl, just wanted to baby him. Turk, the male, was a little less tolerant but only gave a little warning growl and walked away when the pups tried to jump at his face.
If you go back to that house, just look around the yard and it should be obvious if a pit lived there. There should be a path at the fence line and maybe a hole or two in the yard. It may well be that the owners moved and abandoned her so she may need a new home.
I know your babies are very small and you should be cautious for now. And, like you said, you don't know her health history. I would think that Ambrey, being a girl and recent mom, would take right to your babies, though. You have to err on the side of caution but she may fit in better than you might imagine if you have her for a while.
Best of luck to you with her and I hope for a good resolution, whatever it may be.
Jim