Libby Chessler is Westbridge High's popular head cheerleader. A known bully, Libby takes delight in making fun of people she thinks are outcasts or geeks. She particularly enjoys calling Sabrina Spellman (Melissa Joan Hart), Jenny Kelley (Michelle Beaudoin) and Valerie Birkhead (Lindsay Sloane) a "freak" as regularly as possible.
Libby is a spoiled rich girl, who almost everybody, in Westbridge High, sees as a queen. She gives Sabrina, Jenny, and later Valerie, a hard time, calling them freaks, and calling Jenny a "frizzy freak", due to her curly hair. She is turned into a pineapple by Sabrina (by accident) and is later restored back by Zelda Spellman (Beth Broderick), much to the disapproval of Hilda Spellman (Caroline Rhea), who wanted to slice, and dice, her. She is also jealous that Harvey Kinkle (Nate Richert) would rather be with Sabrina than her. She tries to gain Harvey's affections, but fails. When in a very bad mood, Sabrina intentionally transformed Libby into a goat. Sabrina would later turn her back, though some goat-related traits would still linger a bit, afterwards. Sabrina often casts lesser spells on Libby too, usually to amuse herself, or to teach Libby a lesson.
Libby goes for editor for the school paper, in Season Two, only to become furious when Sabrina gains it instead. When Sabrina feels she can no longer be editor, Libby thinks she is going to gain it, and becomes even more angry when Valerie gains it. Libby also has a bond with Mr. Kraft, as they both enjoy giving Sabrina, Valerie, and other students, a hard time. Libby trades places with Sabrina due to molecular instability; Libby is nice and Sabrina tries taking over the world, with her magic. However, Salem saves Sabrina from trials and Zelda switches them back. Libby also tries stealing Harvey from Sabrina, at the school trip to Disney World, but Hilda hides Harvey so Libby can't find him.
Libby also tries stealing Harvey away by taking him to make-out point, but once again, Harvey proves his loyalty to Sabrina.
Sabrina and Salem accidentally fly up Libby's nose and into her brain after being shrunk by Salem's toy. They control Libby from her brain and make her give money to charity, but stop half-way after Sabrina realizes the change has to come from inside Libby. At the start of Season Four, it is said that Libby's parents were sending her to a boarding school, much to Sabrina's delight. However, she does briefly compare Brad Alcerro to a male version of Libby.
- Libby Chessler's character was patterened after Katy Lemore from the 1996 TV movie, "Sabrina The Teenage Witch: The Movie". However, Katy was a senior, and she was replaced by Libby who was a sophomore.