The above image was teased by the official Twitter account for Batman: Arkham City. That sure does seem to be Harley Quinn, eh?
On its own, this might not have much meaning, but when you look over these leaked Trophies for unnamed downloadable content, everything comes together nicely. It sounds as if the add-on could be more substantial and story-based than the previous DLC released for Arkham City. If so, I'm totally in.