As heartbreaking as it is, if she was mine il'd personally take her back, because u cannot take that chance of her attacking and seriously hurting your other dogs or visa virsa, There is also the chance she may never settle down even with training, there4 making it more heartbreaking having to rehome her.

Was she previously living with other dogs? If the answer is yes don't it make you wonder why they wanted to rehome her in the first place?. maybe she was the same with their other dogs? there4 she should really of rehomed her to new owners with no other dogs.

I don't really know the situation but to tell the truth, As i said, If she was mine i really would'nt take the chance how ever sweet she seems.

Good luck in what ever you decide.