From that article: Vandervoort—who left the show at the end of season 7 only to return briefly the following fall to wrap up Supergirl’s story—will be back for one episode (tentatively scheduled to air in October)
It was back in Season 8 that Vandervoort was last seen on Smallville, in the episode Bloodlines. (Here was my review of that episode from way back in November 2008.) At the end of that episode, Kara flew off into space, intent on finding the city of Kandor. Hopefully this one episode will pick up where that one left off! And please ... it's the last season ... let's see her in the costume!
So we have an animated movie with Supergirl in September. And Supergirl on the small screen in October. Too fantastic!