The reason she's going up there is because the order had a part of such because of Fred and George's shop and their excape from Hogwarts. (Set during fifth book, obviously) and she was going up to his room cause she was proud that he had dicided to go to bed early instead of getting drunk. She was bringing him a coffee when she finds out the real reason he went to bed. Oops! She doesn't know that George had even lost his viginity so at first she's shocked and the two notice her while she's still shocked and all George saids is, "Mum." Then I'm stuck.