When she is introduced, Cady is a naive fish out of water, who has little knowledge of social norms in high school and is very behind on pop culture; however, she is depicted as very sweet and kind despite her naivety.

She remains to have a good heart but is heavily influenced by peer pressure throughout the story and longs to fit in,[3] which leads her to become spiteful and plot revenge against Regina George.

However, she is shown to regret this revenge later on and eventually chooses to abolish the cliques at her school and ends the film returning to her original kind and sweet personality, though she is slightly less naive.

The next day, two students named Damian Leigh and Janis Ian befriend her and try to educate her on how to navigate high school, including warning her about a group of rich popular girls dubbed "The Plastics", Karen Smith, Gretchen Wieners and especially their leader and the school's queen bee, Regina George.

Cady develops a crush on a boy in her math class named Aaron Samuels, but is told by Karen Smith and Gretchen Wieners the next day that she can't like him as he is Regina's ex-boyfriend.

Cady throws a party at her house, without inviting Damien or Janis, which gets out of control as she accidentally vomits on Aaron after revealing to him that she had lied about her intelligence.

The next day at school Cady is seen by the principal about the Burn Book, but while this happens a riot breaks out as the girls all see their entries and begin accusing each other of badmouthing them.

Cady finishes the school year dating Aaron, and being friends with Damien, Karen, Janis, Kevin, and Jessica, North Shore now having less cliques dividing the student body.

Benjamin Dzialdowski wrote for BuzzFeed that "Mean Girls is one of THE most quotable films, and Cady's voiceover sets everything up as we join her for the wild ride that is high school.

[13] Aya Tsintziras of Screen Rant said in 2020 that "Mean Girls is one of Lindsay Lohan's most popular films and Cady Heron is one of her most compelling characters.

"[14] In March 2021, Richard Brody of The New Yorker ranked Lohan's performance in the film as the eleventh best of the 21st century up to that point, praising her "blend of charisma and awkwardness, innocence and guile" as well as "faux-casual earnestness" she used for dialogue.