It is very hard to press charges and win on a butt squeeze. Most jurisdictions won't let you even try. They have a lot of stuff in their court systems, and even beyond the fact that culture tends to downplay stuff ("oh, it was just a butt squeeze"), very simple assault of ALL kinds tends to get dropped before court because it takes up time they need for other stuff higher on the food chain.
But the standard for criminal behavior vs. the standard of how to behave as a member of society or as an employee of a large company are not the same. Plenty of forms of sexual harassment meet the standard for "get fired" that are nowhere near "criminal prosecution."
I'm sure we can all think of plenty of behaviors that would get us grounded as teens, fired as grown ups, and thrown out of PTA that don't meet standards of misdemeanor/felony behaviors.
As well, for anyone who says she should have handled it at the time: That's nice for you to say. Very often in these situations, people are shocked into silence. It is hard to speak out at all, but often somewhat easier to do it when you're out of the moment and have time to reflect and realize it was NOT OKAY.