Her name is Heather and she was quite a popular cheerleader in high school. Not the Claire-Bear-saves-the-world type of cheerleader. More like the "bitchy mean girl" type.
This is from Chuck's fourth episode for the second season (Chuck vs The Cougars), which will be set at a high school reunion (Sarah's if I'm not mistaken).
And she is actually Nichole Richie, who auditioned for the character that would be Sarah's (Yvonne Strahovski) nemesis.
Word is, she did quite alright with her scenes.
