Jena Malone who you may know as Johanna Mason from the Hunger Games movies may be in the new Batman V Superman flick. She has visited the set, and the new hair color would be perfect for Carrie Kelley the female Robin character from the comic books. Red hair could also be Harley Quinn or Barbara Gordon (Batgirl), or you know she may just like red hair, and it is a good look on her. Her set visits could also just be that she is good friends with director Zack Snyder, and she just wants to check out one the biggest movies of 2016. Heck I know I would.
Regardless you can read all the speculation over at Batman-news.com.