|“||My beauty intimidates people.||”|
–Sierra, "Pleasant Hills Confidential"
Sierra is, by her own admission, mean and stuck-up. She has her own posse (Jennifer and Claudia) who follows her around and does everything she says. Sierra is the school’s head cheerleader; the squad would fall apart without her.
She constantly competes with Riley for the affections of Johnny Hitswell. In the second season, when Riley and Johnny become a couple, her crush on him persists, and her aim becomes to break them up so she can be Johnny's girlfriend.
Sierra often resorts to underhanded tactics to keep Riley away from Johnny. When Riley got a makeover for the fall dance, Sierra, Jennifer, and Claudia pretend to let Riley join their "cool girls' club", then they shove Riley into a fountain. In "Late Night with Todd & Riley", Sierra apologizes for not inviting Riley to a pool party. Riley invites Sierra to her sleepover, where Sierra creates evidence to make it look as if Riley is cheating on Johnny. Riley catches Sierra as she's trying to escape, and she dumps a bowl of ice cream on Sierra's head. Sierra finally succeeds in "Heartbreak in the City". When Johnny becomes a model, Sierra plants seeds of doubt in Riley's mind, and she convinces Riley that Johnny would dump her for another model. This results in Riley traveling to New York City to confront Johnny; there, Johnny ends up dumping her.
In "Double Trouble", Sierra creates a plan to prevent Riley and Johnny from getting back together. She convinces Riley that Johnny dumped her for a lookalike, so Riley shoves Johnny's date into the same fountain. Afterwards, Riley discovers that Sierra lied to her; the doppelganger is Johnny's cousin, not his new girlfriend. This further sours Riley and Johnny's relationship to the point where Johnny believes that Riley is "no better than Sierra."
Sierra also has another side, in which she is infatuated with a sci-fi show called Star Journeys, which Todd also likes. Sierra never told anyone else before, as her fellow cheerleaders would’ve made fun of her for being a geek. This forges a bond between Sierra and Todd, which doesn't last long when she becomes a cheerleader again (a later episode reveals that Todd still has feelings for her). In the same episode, Sierra gives a rousing speech to her teammates about how they were free to do whatever they wanted now that they were off the squad; her teammates decide to go shopping. Ironically, in "The Means Justify the Trend", Sierra is one of the girls who followed the trendsetters (first Heather Hartley, then Riley) and copied their style, even giving a speech to Riley about how it's her right to copy other people.
Sierra has light tan skin, freckles on her cheeks, long black hair in pigtails, and green eyes. She wears a light red long-sleeved frock with scarlet red patterned stripes on it, and white boots.