Man, what that guy did was gross and wrong, but that mom needs to get off of the hyperbole express.
As a parent, I'd be pissed, but, dude, it sounds like she was a willing participant in this. He's a grody creep, but that mom sounds like a chick who is really embarrassed her 15 year old was messing around with a teacher, and is kind of being kind of obtuse about the whole thing.