    While it was terribly nice of her to get defensive on Ron’s account, it wouldn’t do them any favours in convincing Professor Snape that they had nothing to do with Malfoy’s lateness. The professor probably realized he hadn’t seen Erus until after Malfoy had returned, and whatever Malfoy had said to him had led Professor Snape to the conclusion that Harry was to blame for Malfoy’s lateness.