Belinda Zee is the emotionally unbalance, superpowered doppelganger of Linda Lee, a.k.a. Supergirl. She was created thanks to the machinations of Mr. Mxyzptlk, by way of Supergirl being struck by kryptonite rays. The rays had been filtered through a light projector and created Belinda. At first, Supergirl was excited at the idea of having a fellow Kryptonian, but Belinda quickly proved that she was the opposite of Supergirl in every way. She cared little for both Supergirl and her goody-goody attitude, which she deemed "uncool", and had no interest in being a superhero.
While she is not good, she's really not evil. She's more chaotic than an actual supervillain. Belinda's emotionally unbalanced, highly powerful, and cares only about herself, her popularity, and making Linda miserable. Because, naturally, if Linda wants people to like her, Belinda wants people to hate Linda. She also cannot stand Lena Thorul (actually Luthor), and the feeling is mutual, mostly because Lena is Linda's best friend, a genius, and doesn't worship her like the other students. She has, however, aided Supergirl in one rare occasion.
After establishing her identity as cheerleader captain and one of the most popular girls at Stanhope Boarding School, Belinda made it look like Linda had set up a campaign for student council president, despite the fact that there was no election. The principal revealed that thanks to "Linda's" stunt, there would indeed be an election, and Belinda was her running mate. She then tricked Linda into confessing to her how she felt about being in Stanhope, unaware that Belinda was recording the parts of the conversation that sounded as if Linda was badmouthing the other students. On the eve of the election, Belinda gloated to Linda how she pretty much got everyone to hate her, until Lena's timely intervention
She then attempted to drive a wedge between Linda and Lena by pretending she was Linda's best friend, just to irk the both of them. Around that same time, a meteor had crashed into the school, and many students gained superpowers due to exposure. Belinda revealed her powers to the other students, and when Lena created a device to take away said powers, Belinda went around restoring them with a meteor fragment. This timeline, however, was undone thanks to a time-traveling Supergirl doppelganger, Supragirl. Now, Linda was able to stay and prevent Belinda from ruining her friendship with Lena.
Belinda found herself aiding both Linda and Lena when all the students at Stanhope disappeared. Linda had accidentally revealed herself as Supergirl to Lena while the three learned that a mysterious, super-powered cat was responsible for the disappearances. The three found the cat (named Streaky by Supergirl), and the students, in an alien laboratory underneath the school. While Supergirl and Lena argued about what to do with the students, Belinda got mauled by Streaky. She then informed the others that the cat had escaped in a rocket ship while Lena attempted to stop the lab from exploding. While the other students were saved, the lab did explode. In the rubble, Lena attempted to destroy Supergirl, until Belinda struck her head in a way that erased her memory of the last hour, and Supergirl's secret identity.
Near graduation, however, Belinda's unbalanced fury was unleashed thanks to Mr. Mxyzptlk, who was masquerading as the principal of Stanhope. He played on her desperate need for attention, her joy out of seeing others miserable, and her superiority complex. Mxyzptlk gave Belinda a blue medallion with "#1" carved in it, and upon wearing it her powers were enhanced. She flew around the school using her new "superior vision" to turn the other students into Bizarro-esque zombies, making them "inferior" compared to her. However, upon seeing Supergirl and Supragirl (the Supergirl from the meteor timeline), Belinda turned into "Superior Girl", and attempted to destroy her doppelgangers. Along with Lena regaining her memories of the incident with Streaky and enslaving the rest of the school, the intervention of Streaky (mutated into a giant tiger by Belinda's superior vision), Supragirl warned Supergirl that Belinda was not to get her hands on the communicator which Superman supposedly gave them. Upon hearing them, Belinda quickly stole the communicator for herself as the other two Supergirls dealt with Lena and her brother Lex, now holding Superman hostage. Belinda freaked out when she saw Supergirl's mother in the communicator, technically her mother as well, and the communicator reacted strangely.
Mr. Mxyzptlk revealed his deception to both Supergirl and Lena, being responsible for planting the communicator, creating Belinda, and setting up Supergirl's arrival to Earth. Mxyzptlk made the communicator to act as a collector for Supergirl's emotional energy, but when she wasn't enough for it, he created Belinda to harness her unbalanced emotions. Transformed into a blue crystal statue thanks to her reaction to the communicator, Belinda could still communicate telepathically. However, she was left amongst the rubble of the Stanhope school as Mxyzptlk slowly destroyed the 3rd dimensions, until he was stopped by Supergirl.
Following Mxyzptlk's defeat and the restoration of the 3rd dimension, it was said that Belinda was nearly revived from her crystal state.