Conversation so far:
When did Supergirl first appear in animation?
Supergirl first appeared in Superman/Batman: Apocalypse, a 2010 animated superhero film based on the Superman/Batman comic book storyline.
Was Supergirl never shown in the Superman cartoons?
Supergirl did not appear in any animated Superman cartoons.
Were there any well known voice actors in the animated movie DC Super hero girls?
Grey Griffin played six characters in the animated web series DC Super Hero Girls.
Who were other actors in the animated web series DC Super Hero Girls besides Grey Griffin?
Tara Lyn Strong and Mae Whitman also voice multiple characters in the animated web series DC Super Hero Girls.

Question: What studio produced the movie?
Self-contained rewrite: What studio produced the web series DC Super Hero Girls?