Question: How did Claire get into the closet where Bender was? Vernon locked the door when he left and Bender had to crawl through the ceiling to get out and back in. So how did Claire simply open the door?
Answer: Perhaps she picked the lock.
Claire closed the door once she entered. Which means if she had picked it, then she would have locked herself in. I highly doubt she wanted to perform the ceiling crawl.
Answer: Claire didn't have to pick a lock and the door doesn't lock automatically! It's plain to see: The storeroom door is closed behind Vernon and Bender. As Vernon leaves, he uses the doorhandle and then fumbles around on the outside, "locking" the door without a key. It very much looks as if Paul Gleason acts that there's a working lock. Inattentive viewers may then mistake the door from the next shot for that of the storeroom, but it states: Faculty Lounge. As for "how did she know"? *sigh* How about something so boring that wasn't worth filming it: When Bender returned, they asked what happened and he simply told them! The real question is: How scared must he have been after Vernon's bullying to crawl back through the ceiling (risking another fall) when Claire obviously managed to sneak out and meet him?
Question: Would Claire's sushi, handed to her by her Dad in the morning, still be a fancy treat after sitting at room temperature for five hours?
Chosen answer: The key may have been left in the door knob, Bender wouldn't have known that so he returned the same way he left. Real question is how did Claire know which closet he was locked in?