Shannon - From the series Legally Blonde.

Ah, I understand now which Shannon you mean. You mean the Shannon who acts as a sort of antagonist to Elle Woods during her time at school, not the friend who welcomes her. My previous answer was about a different character, so it was a misunderstanding.
Shannon, with a more negative attitude towards Elle, has a personality closer to the typical teenage rival from Legally Blonde:
Competitive: She sees Elle as someone who could disrupt the school's social balance. She doesn't perceive her simply as a new classmate, but as someone who might attract too much attention.
Haughty and classist: She tends to judge Elle by her appearance, her very feminine style and her way of expressing herself, believing that she does not fit with the image she considers "correct".
Controller: She likes to have influence over her group and maintain a certain order within the school environment.
Sarcastic: Uses double entendres, looks, and small humiliations to create distance with Elle.
Insecurity behind her confidence: Although she appears confident, much of her attitude stems from a fear of losing the spotlight or of someone different being accepted.
Proud: She finds it difficult to admit when she is wrong because she is used to having a position of social power.
Observer: Analyzes Elle a lot; although she criticizes her, she also notices that Elle has qualities she did not expect (such as her intelligence, charisma and ability to connect with others).
Her dynamic with Elle is interesting because Shannon represents the exact opposite of Elle: Elle arrives being authentic, cheerful and unafraid to stand out, while Shannon tries to protect her image and her place within the social hierarchy.
Deep down, Shannon doesn't necessarily hate Elle for being "bad"; she sees her as a threat because Elle proves that someone can be different and still win people over.