Misty's door mechanic has been in for a very long time lol. The door in question is just outside your office to the left, and behind it is *only* Misty. If her door is open and you make too much noise (using the plushie), she will barge into your office and initiate a minigame of "click fast enough for x amount of time, or lose." This attack will happen even if the door to your office is closed.Ah, maybe next time I play I'll try to confirm that the door might enable Misty -- in the most recent update I played the threat of Misty seemed to vanish.
I haven't tested it with the current update, but I know they made Misty super easy in the past, and whenever she triggered, it would reset all other girls to their starting point. That, on top of the fact that time doesn't pause while she's attacking you, meant it was actually *good* to trigger her.