It has long been rumored that Robbie’s Harley Quinn would appear in Birds of Prey, but the DCEU’s roadmap has been convoluted, especially in conjunction with Harley and the Joker.
Margot Robbie’s Harley Quinn has also now been confirmed to appear in the movie.
With that film now stuck in development limbo, it’s plausible the honor will go to Birds of Prey instead.
With Harley now set to appear in Birds of Prey, it’s also possible that the Sirens will face off against Batgirl and Black Canary in the film.