in order to make her stay awake you need to peek at her room where she will be masturbating and not gonna be playing on her computer and after that you will be able to see her staying focused on the class ...
Wait, I've got it to work. I'm not sure what I was missing before but this time when I brought Rachel to the office for punishment it unlocked a new position.
Been a while since full play through, but the missing bit might be the scene where Emily tells Rachel about the DLC for her game. As I recall, a couple other classroom events have priority over it.
