8) Barbara Gordon
It’s already highly likely that Barbara Gordon is on her way to being introduced into the DC Extended Universe, as it’s thought that the part Jena Malone was set to play in Batman V Superman (until her scenes were cut from the theatrical release) was Barbara. Given that, it would be great to see her turn up in some form in a Harley movie.
In the comics, Barbara is the founding member of the Birds of Prey. After she’s paralyzed by the Joker, she takes the codename Oracle and acts as the eyes and ears of the Birds on their missions.
Alternatively, an upcoming series will see her, now back in her Batgirl guise, reform the team. So whatever version of the character DC chose to go with, there is surely a role for her in the film.