Fans of DC Comics often wonder why Supergirl commonly isn't part of the Teen Titans—one of the most famous superhero teams in multimedia. Kara Zor-El is more than qualified to be a part of the team, as she's one of the most potent teenagers in superhero comics. Although she usually helps the Legion of Superheroes, Kara was once, in fact, part of the Titans at one point. However, Cassie Sandsmark, the second Wonder Girl, fired her for a pathetically petty reason.
Even if she's not the most popular Wonder Girl among fans, Cassie Sandsmark is one of the most valued members of the Teen Titans. She joined the Titans with her crush, Superboy, after leaving DC's original Young Justice team. Conner Kent and Cassie eventually establish a romantic relationship, though it doesn't last long. In Infinite Crisis (Geoff Johns, Phil Jimenez, George Pérez, Ivan Reis, and Jim Lee), Conner dies in Wonder Girl's arms. The Titans take some time to heal, but they eventually open to recruits, and Supergirl makes the cut. So why is she fired so quickly?
Supergirl gets fired by Cassie at the start of Teen Titans #55 by Sean McKeever and Jamal Igle. Tim Drake catches a glimpse of Kara leaving as she says, "do me a favor, Cassie. Lose my number." In issue #54, Cassie also reveals that Kara is her best friend, so why does this happen? Cassie goes on a date with Tim Drake and explains why the drama all started. Cassie explains that her future self revealed that Supergirl is only on the Teen Titans to fill Superboy's vacant position. Even though Kara definitely qualifies for the Teen Titans position, Cassie tells Kara she should leave based on her futuristic premonitions. She also says they shouldn't be friends anymore because Cassie now sees Kara as the Kryptonian replacement for Superboy in her social life.
Kara and Cassie eventually make up in Teen Titans #66 by McKeever and Eddy Barrows. They catch up, hang out, and update each other on their costumes. However, the rekindling of their relationship trades another tragic loss. After The Titans realize they've lost too many members, they open to recruiting at least five more heroes. Instead, Tim decides his time on the Titans is over. Tim ends his team status on good terms, but the Teen Titans settle without a Robin. As the team watches Tim depart, Blue Beetle says: "this really, really, really, really needs to stop happening."
DC Comics revoking Kara's Teen Titans membership is understandably disappointing, but at least she got to join the team in some of their adventures. Even if Wonder Girl's emotional healing got in the way of Kara's membership, at least the two made up. The team knows they can forever trust Supergirl, thanks to her neglected history as a Teen Titan.