Technically Belle, Cinderella, and Tatiana aren’t either, they marry their princes. They can never be Queen, only the Queen consort or Regent since they are not of noble birth.
But Mulan, who is already a noble lady by birth, saves her country and get’s adopted by the Emperor, or the Tianzi (literally the “son of heaven” and the “king of all kings”). But she wasn’t a ward of the state, which would make her a Princess (Zhu), as Imperial Princesses (Gong Zhu) are only the biological daughters of the Emperor.
Nope, the Emperor recognizes her as a a part of the army and promotes her to a General (Gong), before adopting her making her a Prince (Wang Zi), the Imperial Princes (Huang Zi) again being the biological sons.
She’s the High and Honorable General Prince Fa Mulan of Han (Han being the name of the Imperial Family, Fa being her birth surname) or Wang Zi Han Gong Fa Mulan.