As Margot Robbie mentions, the Gotham City Sirens are typically a trio of three major Batman femme fatales: Harley, Poison Ivy, and Catwoman. Ultimately Robbie thought it would be more interesting to include a larger team, one populated with slightly less iconic characters. As for Catwoman, Zoe Kravitz will play the iconic character in Matt Reeves’ The Batman, before hopefully crossing over with the Birds of Prey sometime in the future.
Article source: https://www.cinemablend.com/news/2489202/margot-robbie-explains-why-birds-of-prey-came-before-gotham-city-sirens