Students are so different from each other. Emphasize what Catherine brought up: she’s only competing with herself. She didn’t use good practice discipline when she missed lessons due to snow etc., so she will reap the result of those actions in this audition. Her parents need to bring her to at least one extra, paid lesson if she is so excited about playing and doing well. Let the next-to-last lesson before the event be as much like the event as possible, with a stranger there listening, the allotted time given, and you, her teacher, writing down an honest evaluation, even wearing a different hat and calling yourself “Mrs. Brown, the Adjudicator” for example,