Claire is frenemies with Mackenzie. She has a boyfriend, Blake, and she wants to get into Juilliard, as well as Mackenzie. Claire and Mackenzie are always switching off as #1 and #2 in their school's orchestra. Because Juilliard only admits one student from each high school, Mackenzie and Claire have formed a rivalry. However, their rivalry goes deeper than Juilliard. Mackenzie also covets Claire's boyfriend. To sabotage Mackenzie's Juilliard audition, she has Blake do her dirty work for her. He is able to get Mackenzie to tell Blake what song she plans on performing for her audition. Claire's audition is first and she plays the song Mackenzie was supposed to perform. A shocked Mackenzie thinks fast and is able to perform a backup song. Mackenzie then finds out Claire's despicable intentions and the two break off their friendship.
Later, it is revealed that both girls received acceptance into Juilliard. Blake, later, breaks up with Claire, saying that he truly has feelings for Mackenzie. Mackenzie, heartbroken that Blake tricked her, is not interested. At a Juilliard dinner for incoming freshmen, Mackenzie and Claire begin to fight over another boy. Mackenzie ends up winning his interest, but then realizes that she is still in love with Blake.
In The Good Girls, Julie/Parker is on her way to kill Claire for the way she treated Mackenzie. Once Mackenzie figures this out, she hurries over to Claire's house to save her, despite her hostile feelings towards her. Mackenzie gets there in time and Julie/Parker does not kill Claire. When Mackenzie reaches Claire's house to make sure she is okay, Claire's mother invites her in to eat cookies. The two reconcile and the reader is left believing they get over their differences, considering they're spending the next years in college.
- Blake (Ex boyfriend)