At the age of 14, Fanning has already worked with the likes of J.J. Abrams, Sofia Coppola, and Cameron Crowe. But with Sally Potter’s “Ginger and Rosa,” she takes center stage and adopts a British accent to play Ginger, a young girl living in 1960s London. Ginger has a lot on her mind: her parents’ separation, the threat of nuclear war, and the growing distance between her and her best friend weigh heavily on her. It’s a lot for any actor to convey, let alone a teenager, but Fanning proves wise beyond her years with a thoughtful, complex performance.