Someone I follow on Twitter who is a ridiculous Star Wars nerd claims there is info that there is still one more female role to be cast. According to him, the speculation is that is it Assaj Ventress (sp?) from the Clone Wars animated series.
I'm completely unfamiliar with Ventress' story, but wouldn't she have violated the "Rule of Two" for Sith? Also, how would she have survived the purge between Eps 3 and 4? Also, wouldn't she be ridiculously old? I think she was older than Anakin, and if the Solos and Skywalkers have kids that would make her grandmotherly.