Cosette didn't forget the reason she went to the dining hall before the suggestive interaction with Maxen. However, it was too awkward to stay in the same place as him when someone came in. Of all people, Asher had to come, but in a way, she was thankful it was Asher and not Luke. That would be a huge problem.
So Cosette stopped a staff on her way back and asked her to bring some food to their room nicely. Much to her surprise, the servant knew her name. Cosette was a little embarrassed to ask this favor, as she didn't want the servant to think she was acting like a princess. But alas, the servant happily accepted her request.