Sorry to hear about this attack on Lucy. I would try to find a good home for Rosie but I'd never turn to a kill shelter since it seems like alot of people fear pits and she would probably end up euthanized. Maybe an exclusive pit rescue where the rescue people know about this breed and understand that it's all breedism. Until I found such a home or rescue, I'd try to limit time together if I wasn't home. Maybe confining the dogs to seperate rooms while she is out will help and only when she's home that she can be assured she can watch over them to settle any potential fights. Another alternative is maybe just doing the seperationg while out but not rehoming her. I can understand that it'd be hard to give up a dog and as long as they're supervised when together (both dogs or with the daughter), everyone can live peacefully. Good luck to your sister.