I have seen simular behavior in other dogs who are flat out spoiled. The dog is in control 99% of the time, so when you try to do something otherwise, it snaps to get its way. The dog has learned to be in total control. I think undoing the behavior is going to be next to impossible at its current age. Does the dog do this at other times? Or mostly just when you want it to move and you try to move them? If its only when being picked up it could have a hot spot somewhere. I have a Lhasa, who is the best dog, if you pick her up wrong on occasion though, she will yipe real bad. Never bitten, though she has snapped once or twice when she was physicaly hurt. So though she has had a vet check up, its still possible that she is sore somewhere, like a hip or something otherwise unoticable. I would suggest control her in the non-obvious ways as much as possible. Did you read up on the NILIF?