There are apparently "multiple sources" telling The Hollywood Reporter that Jena Malone has a role in Zack Snyder's Batman v. Superman: Dawn of Justice. This is the closest thing to an official announcement from Malone, Snyder or Warner Bros. that we're going to get, I think.
It's been regularly, repeatedly rumored that Malone has got some kind of role in the film; when she dyed her hair, much speculation rushed forth that she'd be playing the Carrie Kelley version of Robin.
I'll believe The Hollywood Reporter's claim that she's in the film 100%, but the Robin thing... only 90%. For now. But those are good odds.
Malone, of course, has a working relationship with Snyder from Sucker Punch.
Batman v. Superman is also rumored to feature Nightwing, who is a former Robin now grown to adulthood.