pitbull rescue turning aggressive towards all humans except me

by d
(maine)

i rescued a 2 year old female pitbull named pip 4 months ago. her past is not known with certainty, however she is covered in scars (including one across her throat from an imbedded collar that had to be cut out of her flesh) and was most certainly physically mistreated. she has had at least 1 litter of puppies, and she is heart worm positive, currently undergoing treatment. it is fair to say she has been through a lot, and still has a ways to go before she's truly recovered, physically speaking.

i'm single and i live alone, and the 1st 2 months with me, pip did great! she's very smart and was house broken within 2 weeks. with crate training, she quickly learned all of the major house rules, and i was able to allow her to move more freely about the house when i was at home. additionally, pip met many of my friends, went on group social outings with us all, and seemed to be a happy member of the group around me and my friends, as well as the occasional other dog.

all of that started to change fairly abruptly around the start of our 3rd month together. one day while i was at work, pip refused to leave her crate when her dog-walker (that she was very familiar and comfortable with) came to walk her mid-day. the next day, she refused again, and growled and nipped at the dog-walker. this was the end of mid-day dog walking services for pip on days that i work.

shortly thereafter, pip started demonstrating issues towards strangers we would encounter on our walks. initially, she started cowering and trying to run away if we encountered a stranger on a walk. quickly, however, this transformed into her barking, growling and lunging towards any and all strangers in her vicinity. and now we're at the point where she barks, growls and lunges towards strangers that are literally hundreds of feet away from us, who appear as tiny little specks on the horizon. she is very strong, and i question my ability to successfully contain her at all times. i am sore and tired from the constant struggle, and now dread taking her out (whereas it used to be a highlight of my day!)

the latest development is that pip, formerly friendly with my friends, now exhibits dangerously aggressive behavior towards them as well, regardless of location - whether we go out to meet them somewhere neutral, or whether they come to our house (her territory) to visit. i don't know what to do. it is clear to me that pip would be most comfortable right now if the world consisted of only me and her. she will not let anyone other than me anywhere near her. this is certainly not sustainable. please advise!!! thank you.