Chewbacca should be the villain.
Leia as villain would be too much I think. In my view, she would never have become a Jedi. Maybe that disappointed Luke. She would be a great leader in the Republic. Sister of the greatest Jedi Luke. I hope the story is interesting and that all characters play a meaningful role even if not wielding sabers.
As for Carrie Fisher's other successes: "When Harry Met Sally" and "The Burbs" stand out.