OH MY! Don't every park your bike at that rack again. If she can't steal the bike, the components would be next and you can't U-lock the derailluer! (sp) Please don't use that bike rack again.
This is the reason I don't use bike racks is due to the fact that people who steal bikes go there first. Always! I hate to say this but I'm one of the few people here that is anti-bike rack for this reason. We have loads of bikes parked at the train station and there are dozens of vandalized bikes there each year with missing wheels, handlebars, peddals etc! The only reason you still have your bike is because
a. The girl knew she was being watched by the owner.
b. She didn't have a bic pen or steel bar to open that U-Lock
You have to hide the bike. Period. Find a place that's two blocks away from the school where it's dark or covered with bushes. Under no circumstances can you leave that bike on the rack. Did you ever wonder why no one parks there? It's probably because that girl and her friends are using that bike rack to pay for their books!