Why does it have to be to do with being turned on, by not locking the door?
I know who is in my toilet... if I don't, id ask if needs be... if no one replied I wouldn't pull out a shotgun and unload a clip into the room and then go... oh damn the Mrs was in there.
Also was she taking a dump at the time? Do we know this for a fact?
Odds are IF she was in there for toilet purposes it was a quick pee... in, sit, pee, wipe, wash, out.... no need for locking in that scenario.
The door was locked for a reason... fear. Not toilet reasons, but fear of life reasons.