She looks very...what's the word? Glamorous. This shot is from the episode, "Expiriment in Error". After having Simon's expiriment fall on her, she pretends to become a zombie to make Alvin feel guilty so he'll take her to the Black and White Ball that he was invited to. Brittany has a very devious personality, just like Alvin.
Alvin and the Chipmunks: The Squeakquel Movie Poster (#13 of 14)
High resolution official theatrical movie poster (#13 of 14) for Alvin and the Chipmunks: The Squeakquel (2009). Image dimensions: 1908 x 3000. Directed by Betty Thomas. Starring Zachary Levi, David Cross, Jason Lee, Justin Long