Any dog would react to that. You should not allow that sort of behavior from a child, ever. That is an excellent way to get bitten. Especially considering that the dog growled first, which is a warning. "Stop that or a I bite". Both you and the child ignored that warning, several times over, and you're surprised that the dog snapped?Last night, she reacted towards my niece. My niece was over here 3 weeks ago and was "hitting" my puppy towards her face a few times.
You could call the vet and see if Proin causes aggression, but honestly, if somebody was doing that to me, yeah, I'd slap their hand away. I can't see this as bad behavior on the part of the dog. She tried to warn, then she snapped without biting. That's a good dog right there.
In the future, do not allow dogs and children to play unsupervised and if you see either one doing something wrong, end the play and separate them.