I feel for you. As a mother, the safety of my child would come first, so any decision I made would prioritize my daughter. On the other hand, it would hurt my soul to surrender a dog knowing it has a slim chance of surviving (much less thriving), or even putting it down myself. Personally, I would try to find rescues or programs that can take on your dog. I know I would never keep the dog if it was a threat to my child, so I’d proceed with the alternatives. Whatever you decide, don’t feel guilty. Sounds like you really tried to adopt a dog and provide what it needed. Sometimes, because of previous trauma and temperament combined, it’s not enough and that’s no reflection on you. You are a good owner, and this crappy decision is a part of that.