Laura, I hope you can continue to keep an eye on this baby and keep her safe, especially if she has kittens or is with kitten. I hope to goodness she doesn't have kittens out on the street.
Could you take her to the vets to see if she is micro-chipped? Perhaps she has got out and that's why she's pregnant or has kittens? It could be an accident.
Please keep us updated about her, she's beautiful. It breaks my heart to think of her being homeless. I hope it all works out (if she keeps coming back for more food and love)