Gotham City Sirens is in the middle of being developed, with David Ayer on the helm and casting for the film can only be assumed is underway, as Margot Robbie is the only actress to be officially attached to the film at the moment, returning as Harley Quinn.
Casting rumors have circled the internet, mostly those by fans, fan casting actresses who they believe will be perfect for the roles of characters such as Catwoman and Poison Ivy, as fans have approached actress through their social media accounts on the idea of them playing the roles. Such one fan did recently with Bryce Dallas Howard, on the idea of her playing Poison Ivy, in which she responded.
— Bryce Dallas Howard (@BryceDHoward) April 8, 2017
This simple reply has led fans to assume Bryce Dallas Howard is in talks or is at least interested in playing the role in Gotham City Sirens, but Howard nor Warner Bros. have confirmed the casting. As of this moment, Gotham City Sirens has yet to have its Poison Ivy and Catwoman.