So from how I understand it, Puppy Pink isn't supposed to appear in or next to the office. Once she leaves Cam I, she's in your office, only attacking you if you leave your cameras up for too long. She doesn't move if you keep the cameras on her though, so to prevent her from coming in, check Cam I each time you flip the cameras up and be quick with checking on the others when she's not in Cam I anymore.
This is such a weird mechanic, but I think it would be better explained to the player if her hand slowly crept from the top or the side of the monitor when it was up, going away once the monitor was pulled down.