Ballerina Princess

The Ballerina Princess is a character in the 2018 Disney film, The Nutcracker and the Four Realms.

Background
According to Sugar Plum while watching the ballet, she explains to Clara that the ballet tells the story of the Four Realms with the Ballerina Princess representing her mother Marie Stahlbaum's discovery of the Four Realms. At the end of the ballet, she was praised with joyful cheers for her amazing performance done during the ballet.

The Nutcracker and the Four Realms
As Clara is presented as the Princess of the Palace of the Four Realms and just as Clara, Phillip, and the Regents take their seats to watch the story of the Four Realms, the Ballerina Princess dances across the stage, just as Sugar Plum explains to Clara that the ballet tells the story of the Four Realms and how her mother discovered the Four Realms prior to her death as the Ballerina dances through scenes representing the Land of Flowers, the Land of Snowflakes, the Land of Sweets, and the Land of Amusements (the area where Marie had her troubles at before her death). As the Ballerina is at the scene representing the Fourth Realm, she retreats from the dancers representing the Mouse King and his henchmen and after the scene, the Ballerina performs pirouettes in solo while Sugar Plum explains that Mother Ginger was the one who began the war with the Four Realms, just as the ballet ends with the Ballerina dancing with background sets of the Lands of Flowers, Snowflakes, and Sweets behind her. She is not seen again afterwards.

Trivia

 * Despite her limited amount of screen time in the film, the Ballerina Princess sporadically appears in many posters promoting the film, especially on the front cover of the DVD, Blu-ray, and 4K HD releases of the film.
 * In the DVD, Blu-ray, and 4K HD menus of the film, the Ballerina Princess is often seen dancing in solo while footage from the film plays behind her.
 * It is unknown if she is affected by Sugar Plum's betrayal to the Four Realms.
 * Her actress, Misty Copeland, previously participated as Clara in the original Nutcracker ballet.