in the book Chani is pretty much fully supportive and goes along with whatever Paul wants/needs to do, but in the movie she's very much not a believer and doesn't seem to trust him, especially by the end of the second movie

Chani was devoted, but not blindly. She was not lacking in intelligence or any other qualities. As such, she wasn't stupid enough to threaten her peoples' chance at fulfilling both the prophecy and the promise of Kynes by openly questioning the mahdi who was delivering both to them. Denis's Chani is the way she is "because boss bitch strong woman don't need no man" no matter how pointless and contrary the behavior is for the situation, which is as much an insult to feminism as characterizing her as a brainless damsel.