I just beat night 6 and have a bit of a strategy
Check the food court and Exbibit 3 cameras constantly, since they're the last cams before she enters your left and right halls. if she's on those cams, go to the respective door and close it, if you don't see her in either by the time you hear a sound, check the vent above you, don't bother with the other cameras.
You should be golden with this, but if you want, close both doors and the vent by 5am, if you do it right, you'll beat the night with this (With or without the 5am lock in)
Edit: didn't read it fully, didn't see they beat it already