Hey there ShibbysMom,
First off, putting her on her back is pretty frightening for a dog, Wolfs only roll other wolves on their backs when they are going to go kill them. So if your rolling your girl on her back when your friends come over you are associating very negative feelings with that situation. With a dog that has been abused, I believe, you should only use positive reinforcement methods to train her. Your her saviour and anytime you scare her or harm her you bring back those feelings of abuse from her previous owner. Since your dog is already a bit aggressive you should definitely spay her it’s just the responsible thing to do as those traits are undesirable for breeding. She sounds a ton like my girl Kenzee. My girlfriend at the time adopted her from the pound but had no experience with pits and neither did I. Her apartment complex immediately banned her when she bit another dog and instantly I had this Pit Bull I had to take care of. She too had been abused by her previous owner and was very timid at first. Then once she got used to her surrounding she became extremely lovable but had problems with strangers. Being ignorant as I was at the time I would punish her for growling and aggressive behavior by shouting at her and grabbing her collar and looking her in the eyes and saying NO! I fealt like such an ass when I finally realized what I was doing to my poor girl mentally. I corrected this by instead just holding her by the collar and giving her tons of lovin when guests were over. I didn’t try to force her to meet the guests just held her with me and baby talked her huggin her and loving her while also greeting and socializing with my guests. After a while she became used to guests coming over and since that now meant she was going to get way more attention than usual she became comfortable and even started seeking hugs from everyone. Nowadays new guests can take a seat next to her on the couch and she will just lean on the them and try to lick them. Taking her to new places has also helped her alot socially, but I have to be real smart not to put her into situations I know make her uncomfortable. It’s all a process but I enjoy seeing her big smile as she becomes more and more comfortable in all sorts of situations.
The best thing you can do is do all the research you can about pit bulls.There are great articles here on this website that can give you some of the tools you need to help Shibby become a happy socialized Pitbull. Just read everything in the Pit Info training section. I did and I can’t believe how much good stuff is in there.