Freeze Girl (Nicole Malgarini) is a girl with cryokinetic abilities, meaning that she can freeze things, hence her nickname. She appears only in two scenes in the movie yet has become a fairly popular figure in the fandom. It's most likely because she has no canon personality and can be portrayed differently. No one is certain what grade she is in.

The first time she is seen, it's when the freshmen arrive at Sky High. She can be seen walking on the grounds, where another student rudely shoots her rear with a laser beam. This provokes her and causes her to 'ice' them, and some other students are heard laughing and cheering her on, "Yeah Freeze Girl!"

Warren Fire

The one that danced with her; Warren Peace.

In her second appearance, Freeze Girl dances with Warren Peace at the Homecoming Dance. He looks at her as she shows him her iced hand, he conjures up a flame and grabs her hand, thus canceling her powers out, and they dance. Because of this short interaction, most fans assume they are in a relationship or at least possible love interests. Freeze Girl is portrayed by Nicole Malgarini.
Nicole Malgarini by Clinton H Wallace

Freeze Girl.