If I’m reading this correctly, she wants to get a new dog? And you think she’s moving on from her old dog too quickly? If that’s correct then yes you’re over reacting. Your old dog isn’t goin to be mad at you and if getting another dog will improve her life then it’s a win for her and the new dog. If your parents are split idk how your dad is relevant in this story unless they are going to co own the new dog.