Forget re-enacting scenes from The Sweeney, for a start. Don’t ignore the situation, though. You and your colleagues could fall victim to her light-fingered ways. Anyway, you’ll find it impossible to resist narrowing your eyes whenever she goes by.
There are options. You could tell her that she’s rumbled, so that she’ll renounce her pilfering ways. Yet then you become party to her insidious behaviour; try explaining that when your boss discovers what you know. Talking of the boss, you could always squeal but, if he’s as adoring of her as he sounds, he’ll take some convincing, especially if you lack evidence. Of course, you could just keep quiet. But could you sleep at night?
So become a whistleblower. Most large organisations offer employees support in these sticky situations, so there should be someone to whom you can talk in confidence.
Failing that, give your personnel department something other than staff surveys to fiddle with. Confidentially report the incident to them; from that point on, it is their responsibility to tackle the issue.