I'd be telling my daughter "sorry sweetie, but I'm going to have to do something about this, it's just not on. I'll make sure they know you didn't want to be involved, but as your mother, I'm not letting it slide."
Then I'd be up there at the school, approach the teacher, let him know your daughter didn't want to say anything but you think as a teacher he should be made aware of his actions. If his response is jerk like, I'd take it higher. It's not a joke and she could have been seriously injured. All it takes is one incident and some poor child will be left with some sort of injury, imagine if he caused a spinal injury, wouldn't be so cool then.
Definitely, say something. Apologize to your daughter, one day she'll get it.