Maxine's arc was done later, you need a lot of other stuff to be finished:
Debbie has to be a prefect already.
You also have to spy on Rachel (twice), Cassandra, and Amy on nights after giving them private punishments.
I had a situation on one playthrough where Amy didn't advance because Cassandra misbehaved in class, and I guess her advancement took precedence somehow. It also may have been me screwing something up. Took me a couple weeks of gametime before I realized Amy hadn't advanced.