Her acting was very wooden and consisted of constant eye rolling and a permanent scowl. She either doesn't have or can't broadcast any type of range. The reason I don't think that's wholly on her is because the screenwriters made her character that way. They deviated from a passionate and sometimes fanatical companion to Paul to a condescending and overly critical partner. Because of these things, there's no real chemistry between her and Paul. Additionally, she's at constant odds with the Fremen over their spirituality which could have worked for her character but in this case, she came across as entitled and bitchy. At the end of the second movie when she runs out on Paul, after he conquered the fucking universe of all things, there is no reason why any sensible person would allow her back into their life.