Fisher, Hamil and Ford's roles in the new film may be more than mere cameos.
Carrie Fisher, the actress best known for her portrayal of Princess Leia in the original Star Wars trilogy, is not known for her ability to keep a secret. She previously spilled the beans on the fact that she, along with Mark Hamil and Harrison Ford, would return in the upcoming Episode VII, though many assumed it would be a cameo role of sorts, as a final send off to the original cast. Now, Fisher has said that she will spend a full six months in London filming for the movie, which certainly suggests more than a cameo.
"I'm going off to London for six months to film the new 'Star Wars' movie," she reportedly told Jim Jeffries, who said on the Opie and Anthony show that "And I don't think from looking at it, the new 'Star Wars' movie is a direct continuation. It's number 7 but it's not going to be the next day, I'll tell you that much. Maybe she had the same problem the Emperor had, I don't know."
This aligns with some reports we heard earlier that J.J. Abrams' and Lawrence Kasdan's rewrites of Michael Arndt's script wanted to keep the trio front and center in order to give them a proper send-off, while subsequent films will feature the new younger cast more heavily.
As for what possible role Fisher's character will have in the new film, In the expanded universe, Leia is a founding member of the New Republic after the collapse of the Empire. She also begins exploring her connection with The Force, eventually building her own lightsaber
Source: Screen Rant