It isn't about dominance it's more about fun. For one reason or another the puppy has discovered entertainment value in harassing her over you and your son, likely because you or your son are more likely to give him a negative consequence for the behavior or because you two just don't squirm and give responses he finds entertaining. I'm guessing the first option since he tones it down when you're around, but he might just divert more attention to you guys and harass her less because his attention is elsewhere.
Either way it's fixable through management or her redirecting the pup and tiring him out. He wants to play with her that much is clear.
Swatting him if done lightly he might just think is part of the game. Some puppies like that kinda crap and get really into it. I know this sounds like blaming the victim here but she's bringing that response down on herself.
Last edited by Baillif; 09-30-2013 at 01:51 PM.