I disliked how book readers dismissed or dislike how movie!Chani is portrayed, especially the part how they don't like her walking out after Irulan bargain Paul for their marriage. Other than being different between movie and book, there's a reason why will not accept being a concubin, one crucial aspect of movie! Chani ideology.
Even though Chani and Paul loved each other, there's a massive power dynamic between them. When Paul arrived on Arrakis, he came as an heir of House Atreides, his received the planet as his fief, his ownership. Though he's a far better Lord than the Harkonnen, he is still an Outworlder, a non-Fremen controlled Arrakis. And by the of part 1, Paul inherited Arrakis.
Chani stated in part 2 that all Fremen are equal (there's still misogyny in her culture but still), which it is imperative for her. However, as the story goes on, we see how Paul, even though he loved Chani and appreciated the Fremen, started his domain over them. We saw it firsthand when he acquired his family nuclear warheads, allowing him to cause a nuclear holocaust on the planet and, most importantly, controlled the spice. Other than how acute spice is in her culture, Chani is angry that Paul will controll over her people. And reminded how inequal their relationship was.
And this continued as he embraced his dukeship and challenged the Emperor for the throne. Paul was using Chani's people as his personal army, using Lasin, a prophet that Chani despised, to take advantage over them. When the duel between Paul and Feyd happened, when Feyd called Chani "his pet", she was cruelly reminded where she stands in their relationship, especially where Irulan betrothed Paul. Readers said that concubine is acceptable and tolerated in the Imperium, but a concubine (and usually women) are inferior in their marriage and not in equal standing. This is one of the reasons why she walked out because she will never be equal to Paul, politically and culturally.
