Belinda is a girl that bullied Kara when she was young. That earned her the nickname Belinda-the-Bully. She constantly teased and mocked Kara.
Trivia
- She is a reference to the comic book character, Belinda Zee a.k.a. Superior Girl, a villainous doppelgänger of Supergirl from the series, Supergirl: Cosmic Adventures in the 8th Grade.