My Sister and Her Dogs

My Sister has had pit bulls for years and has never had a problem. Well no problems until now. She has 2 full pits and 1 pit mix that have not until now been any problem.
The one pit which is 7 months old bite her in the face the other day when she was trying to move her on the couch. It worries me so much for her safety. I don't really have a question just talking. The reason she has three is that the first one was companion to the older one she lost last year after 12 years. All of them have been rescues for bad homes.