Chani is not a terribly important character in the books, though she is Leit Keynes daughter, who they race/gender swapped in this movie. She is Paul's consort, advisor, bodyguard. She's his wife in all but name, but rather like Leto I and Jessica, Paul doesn't marry Chani, he marries Princess Irulan (Emperor Corrino's daughter) to make a political marriage and further legitimise his claiming of the throne. Chani is Paul's love interest, the woman he is destined and pre-determined (by his visions) to be with, and the mother of his children. Her storyline is not as interesting as (say) Alia's in book 3, and it would be a mistake for Villeneuve to focus too heavily on Chani. She's a supporting romantic character, (taking for granted that every Fremen character is also a ferociously dangerous combat expert who knows how to live in the deep desert of Arakkis).
Chani's main job in the storyline is to fall in love with, and give Paul an heir. Their first child is killed in a Harkkonen attack. After that, Irulan is secretly poisoning her to prevent a pregnancy. Irulan thinks that if Chani never bears an heir, then Paul will have to turn to her (something Paul has vowed never to do. Irulan is purely a politcal convenience). Chani eventually bears twins Leto II and Ghanna, after going on a Fremen diet to aid pregnancy (and thus unknowingly avoiding Irulan's poisoning). Chani dies of complications after the birth (thanks to Irulan's poisoning), and then becomes an existential temptation to Paul after the Tleilaxu offer to bring her back as a Gola (clone with all memories intact). Paul refuses this as it would interfere with the progress of the Golden Path, and place him in the power of the Tleilaxu, along with accepting a possible trojan horse in the form of a resurrected Chani who might have been reprogrammed to do anything by the Tleilaxu (who are another powerful faction in the Dune universe, specialising in biological technology and have created convincing golas of Duncan Idaho and their own failed Kwizatz Haderach).