From the first moment that we saw the new Mulan in the first trailer it was clear this story would be different, if only because, when we saw Mulan on the battlefield, we saw that she had long flowing hair. In the previous Disney version, in a brief but iconic moment, Mulan uses her family sword to chop off her hair before attempting to impersonate a man.
Article source: https://www.cinemablend.com/news/2490623/dont-expect-mulans-hair-to-be-cut-in-the-live-action-remake