I agree that darkness in a school bathroom does not lead to crime. Can it happen? Sure, but that’s a stretch.
Disagreeing the keyed switch idea as a way to reduce your taxes is like worrying about a pinhole in a waterbucket that’s already been turned upside down; there are much better ways to reduce taxes than keeping bathrooms in the dark. Typically, fluorescent or CFL lighting (see title 24 of the California building code) is required in many commercial and educational spaces, to increase building efficiency and consume very little power. Title24 also has minimum guidelines for plumbing, fire, etc, but those doesn’t apply here. Laugh if you want, but it’s actually a good read. It’s a pain in the ass to live up to so many guidelines and requirements, but if title 24 didn’t exist, I can only wonder how much more in the hole California would be.
It sounds like the OP had good intentions to consider all-time lighting in bathrooms. His wife did or nearly got hurt in the dark, which can probably happen again to someone else, but maybe worse. That’s enough for me to at least consider some ways to improve the safety of the school.
One other option to consider is to use night lights that have built in light sensors, these could plug right into a standard wall outlet.