User blog comment:Oyaya/Future Young Justice members/@comment-3465526-20110822041609

Wonder Girl wasn't included because when they were writing the episodes, there were legal issues with the use of the character in television -- because the legal situation was unclear, they were refused permission to use her. That has since been corrected, but too late for her to appear before the end of the first 26 "season 1" episodes. You should (likely) expect her to show up in the season 2 mini-series "Invasion" that will start next spring.