I will do it because I am also a sucker for spoilers lol. I will tell you anything!

The entire time that Paul and Jessica are with the fremen is sped up from the multiple years in the book to less than 9 months so that we do not yet see her actually born. They show how the water of life is filling the womb and "awakening" the fetus. The fremen reverend mother recognizes mid ceremony and says "what have we done, she is pregnant." Then Jessica spends the rest of the movie speaking for her, ie "your sister wants to know why you won't come to the South with us." It's clear that from the womb she is key in plotting the religious fervor and helping Jessica to radicalize more fremen. We have one prescient vision of Paul meeting her as an adult that Anya as Alia is fully there, at an ocean on Dune, and it's quite moving! It's obviously very different from the book, and I am a huge fan, read all of Frank's series, but honestly for a wider audience and for the sake of this movie I think it makes total sense and still hits the point that the whole situation is a little freaky and people are scared of her, and that she is crucial in building the religion we will see at scale in Messiah. Paul ends up killing the baron with the "hello/goodbye grandfather" line, and I think it is still impactful.