Girls who do not wear jean/denim skirts for tznius reasons are definitely in the ranks of those who understand tznius in the spirit of the law, and it is an admirable sensitivity.
I have formal education in Fashion Marketing, and would just like to let you know that in the Fashion industry the “jean/denim” material is used to connote a certain theme which is against Torah and Halacha and the core of our Jewish value system.
So whether or not you personally associate jean/denim with improper shall we say taavos, the material has been produced and mass marketed for years with those intentions (ask anyone in the fashion workforce, they make no secret of this).
Not wearing jean/denim skirts is not a crazy unnecessary chumrah, that is practiced by those who are needlessly “restricting” themselves. It is a reflection of a true understanding of tznius as not only a list of rules, but as a defining factor in the life of a Jewish woman.