Sometimes when I go to a clients home I prefer to rely on my instincts as opposed to knowing too much, but this puppy has a wonderful story and was adopted by a wonderful family.
She was used to getting her own way in a very short space of time. The children are afraid of her because she is mouthy. Her teeth are sharp .... she is teething. Teeth are breaking through and that hurts dogs just like any child. I always say "Don't humanize your dog" but this is as close as you can get to understanding this behavior. Expect it, it's normal.
What struck me the most as the day went on, was not anything to do with the mouthy nature, but the fact that I learned the dog was incredibly fearful of SUV's !!!