OK. While I believe that school employees can be very inappropriate (and have seen this in action), I'd be careful about taking the kid's word for it. Sometimes, kids can make stuff up, and I've seen that too. I'm on the fence until there are credible witnesses. If kids don't like a sub, a teacher, a bus driver, or a principal, they can be very nasty and some have no ethics whatsoever. I remember one accusation in particular--a career ending and possibly prosecutable accusation--levied against a thoroughly innocent (and overworked) Special Ed teacher by a student who got sick of being scolded for bullying other kids.
If the bus driver did this, then fire her without a retirement. But, let's see if this kid is truly a nice kid with a discerning mind or a little a**hole.