Why did claire danes quit Titanic because of Leonardo?

Maybe Claire felt that she was not suitable for the role, so she said she didn't want to work with the same actor anymore. Kate's role has long been chosen, and Leonardo later said that he participated in the play partly because of Kate. Cameron was going to choose a new generation of stars to play, and Claire would of course audition. More than 100 stars auditioned for Ross.

2. Kate was the youngest nominee for two Oscars at that time (Claire seems to have never been nominated). She was very classical, and Claire gave the impression that she was too pure and unsuitable.