Dinah Lance made her animated debut in Justice League Unlimited, however she almost became a part of the DC animated universe well before that - she was slated for an episode of the fabled Batman: The Animated Series. But it was not to be, thanks to mandates that the show needed fewer canaries, and more... well, Robins.
Image: Warner Bros. Animation
The tidbit was revealed by BTAS writer Paul Dini during an interview with Comic Book Resources about his new Kickstarter-funded graphic novel Boo & Hiss. Apparently, the second season of the show would have seen Dinah make her debut in an episode focused on her and Catwoman, but according to Dini, it was cut thanks to a Fox mandate that the show spend less time focusing on side characters and more time on the Boy Wonder's adventures with Batman:
Yeah, the Black Canary/Catwoman episode was a casualty. They wanted more Robin in the series, and each time we wanted to drop him from a story, we had to fight for it. Not that we had anything against Robin, we just wanted to stretch now and then and do solo Batman stories or episodes that focused mainly on Gordon or the villains. After the experimentation of the first season, the network felt we might be leaving the boys behind, so we got the edict, add more Robin.
Dini also mentions an almost-episode that would have revolved around Swamp Thing and Poison Ivy, but while that was scrapped too, ideas for it eventually made there way into Dini's current DC project, Justice League Action. Alas, plans for a Canary/Catwoman teamup never materialised elsewhere, but at least Dinah finally got her animated dues in Justice League Unlimited.