There's an fairly easy way to free Harriet in Phantom of the Operating Room. The tactic is similar to freeing Wavemaster. Skip the intro video as early as possible, right click one of the kids and use the 'go to' command to get to the correct room quickly, and get a ghost to cast tremor (I've used both Stonewall and Quiver to do this successfully). If you're fast enough, the thief will drop the toy in the room that he starts in and Harriet will be freed almost immediately. If the thief escapes, restart the level and try again.