I am so sorry to hear about this situation. I do have to ask, in lieu of the first incident, what was done following that to counteract the behavior? And when the animal control officer came to the door (she was at the door, correct?), and your daughter went out of the door…had your daughter been taught to know how to best handle the dogs? Especially when “strangers” are at the door, keeping the dogs sitting/staying until they were signaled all was well? I know our pit is extremely protective, since being in our newer house. He doesn’t like the door bell or people knocking much, but I immediately make him sit/stay until I answer the door and/or the person is invited inside.
I have heard, sometimes, where, as you described, your dog had shown no aggression whatsoever before these incidences. But then, when reaching a certain age, usually around 2 or 3 years old, the adult mentality begins to shine, sometimes being overly protective. I am not an expert by any means, but seeing as how there had been two incidences, and although you describe them as “nips” and not “bites,” do what you can with the animal behaviorist, but be prepared to receive other judgment. I will be thinking of you!