Cassie's real name is Cassandra Sandsmark. Her mother is the famed archeologist Dr. Helena Sandsmark. She's a student at the St. Elias Academy For Girls in Gateway City. She is the president of the school's "Wonder Woman Fan Club." She only appears in Teen Titans Go! #54 and #55 but never in the animated series.
In this iteration, all of Cassie's powers come from artifacts her mother managed to acquire. She wears the Gauntlet of Atlas, which allows her to lift great weights, and the Sandals of Hermes, which allow her to move at superhuman speeds and fly.
In her debut issue (which ironically was the next to last issue of the comic series), she claims herself as Wonder Woman's sidekick, decrying Wonder Girl as a worthy one while Wonder Girl is hosting a athletic event on Paradise Island. The event is interrupted by Trident, forcing the heroes to defend the island. She manages to save Wonder Girl from a Trident sneak attack, allowing her to finish him off.
Afterward, Cassie is deemed to have potential and invited to be trained. However, she gets a call from her mother, who grounds Cassie for taking the artifacts without her permission.
She's last seen in the final issue in a dream of Cyborg's as one of his training recruits.