Your granddaughter is playing Russian roulette with that adopted “previously abused 4 yr old female Pitbull”, IMO. I hope and pray that dog never turns on her or anybody else. That said I do hope she is extremely vigilant with that dog.
Stupid. Just no. If you live way out in the country and you own some land and you've established yourself as an "alpha" to the pitbull. Then maybe, go for it. Knock yourself out. Not good for families. Animal shelters should put every pit bull to sleep. They're not fit for adoption.
She knows it makes me nervous. She’s really good with the dog so I hope it works out. The good thing is, even though I don’t approve of it, is that she lives with her boyfriend and he’s a big guy. I’d worry more if it was just her and the dog. She volunteered at the shelter when she came from and knows the dog but sometimes, I wonder if anybody really knows them. I have never personally known a mean Pit, but I know they do flip out more than other breeds.