well, if we want to play make believe, maybe the girl was lying and showed no concern for hitting the little boy?
Assuming that you are correct, the mature, adult way to handle the situation is not to slug the girl two to four times in the face, but to turn her over to the ski patrol or some other person of authority. I've been to these mega ski resorts on many, many occassions and the ski patrol and mountain police are all over the place, especially during holiday week.