Leia's role in The Force Awakens has been largely unexplained. We know shes a general of the Resistance, and... that's about it. In an interview with J.J. Abrams, IGN learned some new details about Leia and the force.
J.J. asked George Lucas himself about an age limit on learning to use the force. Apparently George said, there is none. How does this affect Leia? "Why did she not take advantage of this natural force strength that she had?" Abrams asks. He then answers, "It was simply a choice that she made", she made the decision to "run the rebellion and this resistance" instead of training as a Jedi. But don't loose hope in seeing Carrie Fisher in a light-saber battle just yet. J.J. goes on to say, "she's still force strong" and "it's an intrinsic piece of her character."
In the now discarded expanded universe, Leia began training with Luke shortly after the Battle of Endor. J.J. has in effect confirmed that this hasn't taken place. But like I said, there's still time for her to learn.
In other news, we've all been wondering for a while now, what role will Billie Lourd (Carrie Fisher's daughter) play in The Force Awakens? People Magazine has released some official shots of Lourd's character in the movie.
Who is she playing? Your guess is as good as mine. That's all it would be anyway, a guess considering all we've officially been given are pictures. It looks like she's in the resistance base from other pictures we've seen of Leia and C-3PO. But for now all we have is pictures.
If I am going to guess who she's playing though, my money is on Lourd playing Winter, Leia's trusted assistant in the 'Thrawn Trilogy'. If you haven't heard of Winter Celchu, here is her Wookieepedia page. I'm hoping she's playing Winter. That would be a nice homage to the novels by Timothy Zahn. What do you think?