There's only so much she could have done though, right? Surely every employee has some responsibility to know when they should leave as well. The person closing up can't be expected to check every nook and cranny for an employee who has lost track of time.
I can't hear announcements when I'm in the freezer or cooler in my store, and I've often lost track of time. If, for whatever reason, I was working in there near the end of the night, it's totally possible that I could be locked in without anyone knowing. So it should be my responsibility to make sure that I can follow what's being said/done, right?