From Comicbook.com
On Leia -
"Of course, wee can't tralk about the cast without talking about Carrie Fisher. The character of Leia is really the heart of this story. We realized we could not possibly tell this story without Leia. We had footage from Episode VII so that we could use in a new way. So, we were abler to use Carrie in a new way...we started talking about this movie and I was not supposed to be here. We lost Carrie, heartbreakingly, she passed. I was working on this film and I realized we needed Carrie in this film...She was sort of like always supernaturally witty in a way. I went back and I looked at her last book, the Princess Diarest, she had written and special thanks to JJ Abrams for putting up with me twice. Now, I had never worked with her before force Awakens and I had not signed up for this yet. Now, it was a classic Carrie thing, to do something like that and we could not be more excited for you to see her in her final performance as Leia. "