WOW she is stunning.
It sounds like she's fairly well taken care of. Could it be possible that perhaps her family moved (and took her) and she escaped to try to "go home" ? I've heard of this happening a LOT with cats. Not so much with dogs, but I suppose it's possible.
I really hope that if there is someone out there looking for her, you are able to find them. Thank you SO much for taking care of her. A lot of people would just run away from her because she's a pit bull...this just goes to show that they are sweet hearts too!