Would just like to say (albeit a year late!), what a responsible dog owner you are. In my opinion, how Mully acted was in no way your fault, some dogs just turn like that, no matter what the breed. Mully, her pups and your other dogs are very, very lucky to have dog owners like you and your partner. Most people would sell the dog on for profit.
This world would be a far better place if there were more like you, and dogs would have a better life, too.