This is a hilariously vague answer, but possibly either Land of Oz, the 1910 Selig Polyscope Oz film.
I say possibly, because according to Wikipedia, the film is only known by its catalog description
The Emerald City in all its splendor with all the familiar characters so dear to the hearts of children - Dorothy, the scarecrow, the woodman, the cowardly lion, and the wizard continuing on their triumphal entry to the mystic city, adding new characters, new situations, and scintillating comedy. Dorothy, who has so won her way into the good graces of lovers of fairy folk, finds new encounters in the rebellion army of General Jinger [sic] showing myriads of Leith soldiers in glittering apparel forming one surprise after the other, until the whole resolves itself into a spectacle worthy of the best artists in picturedom. Those who have followed the two preceding pictures of this great subject cannot but appreciate "The Land of Oz," the crowning effort of the Oz series.
However, the description mentions General Jinger, who is based on General Jinjur from The Marvelous Land of Oz, a story whose primary character is Tip, a boy who is later discovered to be the transformed lost Princess Ozma. So it is entirely possible that Tip/Ozma is present in this film - but we don't know.
The Marvelous Land of Oz was also adapted into The Land of Oz, a Sequel to the Wizard of Oz by Meglin Kiddies in 1932. Tip is definitely in this one, but so is Dorothy, so it's not quite a faithful adaptation, and the fandom wiki I found doesn't believe that the Ozma reveal made it into the movie. It's hard to say for certain, because this film is partially lost too.