However, this rumor goes beyond just Billie Lourd playing her mom’s stand-in in the film. This is firmly in the realm of rumor and speculation at the moment but, if true, it could constitute a spoiler, so proceed with caution.
Article source: https://www.cinemablend.com/news/2471952/new-star-wars-the-rise-of-skywalker-rumor-claims-billie-lourd-is-carrie-fishers-stand-in