Susan had been sitting nervously at the Hufflepuff table through all of dinner. She barely could even eat anything. Being the mild mannered girl she was, she had never had an audience with the Headmaster for disciplinary action. Really, the incident with the DA was the only time she'd ever been close to having broken the rules.
She saw Dumbledore go into the antechamber and figured she should follow. She waited a few seconds before departing, but made her way rather quickly. Somehow this probably had to do with Harry, Hermione, and Ron, but she still felt somewhat guilty.