She's an antagonist in the story and is somewhat of a bully. However, she is heavily influenced by peer pressure and deep down isn't a bad person. She is known to be rude to her classmates, but can also be manipulative (able to stay out of trouble by deceiving others into believing she is the victim.) She feels the need to put others down in order to make herself feel superior to them.

Her voice should be somewhat bitter and jealous, over-exaggerating a lot and getting upset when she is upstaged or overshadowed. I imagine her to have a mid-ranged voice, but I'm open to whatever is most comfortable for you (as long as it fits the character.) She should also be able to put on fake voices in order to manipulate others (friendly, sad, offended, etc.) Emphasis and articulation on insults is probably the best way to deliver her lines, conveying anger without necessarily yelling every time.