Your sister got it right. It wasn't the dog's fault. I am actually rather surprised that she stepped into the middle to stop the fight. When dogs get into a fighting frenzy, they do not quite differentiate between friend and foe. The recommended way to stop a dog fight is to hit them with a pail of water. I mean hit them with the water not the pail. Truly your sister's injuries have got nothing to do with the dogs being Pit Bulls. If she had stepped into the middle of a cat fight, she would have got injured, too.