Quite bad.

She's a pouty girl boss in the film (not in the books). She has this weird "anti Paul" thing where she's suspicious of Paul and doesn't trust him to lead the Freman (completely contradicting the fact that he's their messiah and he's also her lover). There is also this weird jealousy thing at the end of part 2 when Paul proclaims he will marry Princess Irulan. In the books she understands politics (and the Freman are polygamous lol), but in the movie she's all offended and jealous.

Idk who's fault it is. Maybe Zendaya was directed to portray Chani this way. But it's essentially a completely different character. She's a nuanced character in the books. In the film she's just another Marvel girlboss.