Leslie was mainly Jess' polar opposite. She was talkative, openly social, cheerful and more open-minded about the world around her and while Jess is poor, she was rich. At the beginning of the movie and book, she was the new girl who dresses different, talks different, and does not play by the same social rules as the other kids do. She beat Jess in a racing event he trained for all summer, but she still tried to compliment him and offered him friendship, but was brushed off. After telling the class she has no television and being laughed at, she tried to sit in the back and he grabs her not a second sooner and starts their initial friendship. Running into the woods, they swing on a rope and start a world of their own. He seems to have some trouble excepting she has different beliefs than him such as his Christianity and her agnostic views. After he leaves her behind at home she attempts to go to Terabithia, but the rope breaks and she falls, hits her head on a rock, and drowns. She leaves him angry, heartbroken and feeling it was his fault she died, thinking if he had invited her or turned Miss Edmunds down, she would not have died.
Leslie recently moved to Lark Creek with her parents. She is a tomboyish, smart, talented, and outgoing girl. Her talents include creativity and running. She can run faster than any of the boys in her class. She was not socially accepted by the other students in her new school. She and Jess are outcasts at their school. He thought highly of her, and was best friends with her (and, possibly, first love). He gives her a puppy whom she called Prince Terrien, or P.T.
Jess has a crush on his music teacher, Miss Edmunds, and would do anything to be with her. The central crisis occurs when he accompanies her to the National Gallery of Art in Washington, D.C., and Leslie goes to Terabithia alone (not seen).
While Jess is away at the museum, Leslie tries to swing across on the rope to Terabithia. As she is doing so, it breaks (as he warned her it would) and she plummets into the creek, hits her head on a rock, gets unconscious, and drowns. This deeply shocks Jess, who considered her death his fault, as he had considered inviting her to go to the museum with him and had decided against it so he could be alone with Miss Edmunds. It was then that she tried to get to Terabithia alone, ultimately the cause of her death. He can overcome his grief only with the strength and courage that his friendship with her has given him. He must trust in what she has taught him to help overcome the horrors that reality can bring, and with their friendship, it helps him to cope with the tragedy. Their friendship makes him realize what she has also taught him, to open his mind to every possibility, and leave reality behind.
Jess attempts to deal with his grief by going back to Terabithia, and making a memorial for Leslie. He worries that she will not enter Heaven because she does not believe in Jesus and that God will damn her to Hell. Jess hears a cry for help, and finds his younger sister, May Belle, calling for help. She was trying to get to Terabithia by climbing on a tree bridge over the river, but got stuck in the middle. He helps her out. She wants to go to Terabithia, but he snaps at her and tells her it only belongs to him and Leslie.
When Jess' father, Jack Aarons, follows him into the forest, he begins to cry, and Jack hugs him. He expresses his worry about her through his sobs, with Jack comforting him.
Leslie's equally grief-stricken parents decide to move back to their old town. Before they go away, her father, Bill Burke, tells Jess that she loved him and thanks him for being such a good friend to her.
- Leslie's death is often considered by many literature fans as one of the most tragic in all history. It was her death that also awarded the book with a Newberry Medal.
- Despite having drowned (off-screen/off-page) in the movie and book, Leslie has achieved a strong fan following, largely due to AnnaSophia Robb's portrayal of her.
- In the book, Leslie is based off of Lisa Hill, who was best friends of Katherine Patterson's son who died after being struck by lightning. According to Patterson, it took a while to work up the courage to kill the girl she had written back to life.
- Leslie is also the title of a song by Austin, Texas pop band The Sour Notes, inspired by her rope swing accident while entering Terabithia.
- In the book, Leslie is a brunette.