That sucks, she does sound like a d-bag, maybe on a little power trip. But there's not a whole lot you can do about it. Well, outside of saying adios. It sounds like it was a loaded question. If she wanted you to stay later she should have just come out and asked you to instead of playing games.
I'd imagine that not too many of your coworkers have any respect for her either since they see what's going on. It'll be good experience learning to cope with incompetent bosses.
Unless you just get fed up enough that you want to move on. And even then, it's generally best to leave on good terms rather than MF'ing her up in down.