It might have gotten her under control. Though some children are so strong-wiled it takes quite a battle before they'll submit to parental authority.
I agree the scenario you mentioned isn't hard. Good children can have bad days and good parents can have difficult children. What gets me is that the girl was hitting her parents. It always amazes me when people let their children hit them.
Funny how the parents who don't believe in spanking are the ones who allow their children to hit them. A child isn't going to strike or hit his parents if he realizes that the parent would spank him in return.