With Batman v. Superman just over a year away rumors come and go. We have heard casting, plot, and even specific scene rumors, and every once and awhile I go back to look at some of the ones that weren't looked at very much. While doing this two potential details stuck out to me the most. Months back people saw Jena Malone in Detroit with Director Zack Snyder. This caused a flood of "reports" that she was now in the film. Now we know that she is indeed in the film, and that she is in a unannounced role. One guess is that she is playing the female sidekick Carrie Kelly, Robin. This is a possibility since she has dyed her hair red, and known to have kicked butt in other films, including Snyder's Sucker Punch.
It is also suspected that she is Robin because a extra on set said that Robin is in the movie, and Robin is female. This is a perfect time to use "take it with a grain of salt," because there is no other proof that she will be, but I do believe this role is a high possibility since a Robin Easter Egg has been scene on set. I don't know if that was from the filmmakers, or a random person who is trying to start a nerd-gasim; however, if the filmmakers didn't do it they would have probably removed it.
Now going off of the hypothetical that Carrie Kelly is in the film, I have a theory about how she will be portrayed in the film. I will put the rest of the Article in spoiler blocks, since it will involve potential spoilers.
Three months ago there was a report that a scene was being shot with Bruce Wayne at a MMA style fight. This was again leaked by another person working on the film. It was said that the scene that would show Bruce in an area not many billionaires would be causing him to have to explain that he is "kind of a night person."
As someone who is constantly looking for news relating to Dawn of Justice, though I kick myself for possibly ruining parts of the movie, I have not seen any reports that would indicate why he would be their. This scene almost seems like a throwaway, and it made me think for a while. Once the news broke that Malone was in the movie I had a thought. What if Carrie Kelly was the reason why Bruce goes to the shady MMA fight? This might seem like a stretch, but it would make sense.
After Batman and Robin, one of the worst films of all time, it would be hard to make Robin believable, especially after seeing the Nolan age. So what if they made Robin completely different from the comics, but used a version of the character that is only really shown in one graphic novel (The Dark Knight Returns) to not anger fans of more popular Robins. So they could change Carrie from 13 to 20, and make her a little more modern. Then have previous Robins be teased in the universe (like a certain suit in a certain cave). Carrie could be a professional fighter by day, but at night she goes out and fights crime inspired by the return of Batman. Causing Bruce to track her down to where she fights, and when she leaves he tells her to stop. Anyone who knows Carrie at all would also know that wouldn't stop her. So maybe after an unprepared first fight with Superman she finds him and helps him, like in The Dark Knight Returns with the mutants. This could lead her into being the Caped Crusader's right hand girl in red.
Again this is all speculation, but I would love to hear thoughts from others so...