Park made her stage debut as a rat in the retinue of the wicked fairy Carabosse in "The Sleeping Beauty", the ballet staged by Ninette de Valois for the reopening of the Royal Opera House in 1946, a year after the end of World War II in Europe. From 1955 onward, while still a member of the "corps", she was assigned numerous solo roles. At the age of 19, she danced the role of the carefree Milkmaid in Frederick Ashton's popular "Façade" in the opera house's Silver Jubilee gala on 6 May 1956. Soon thereafter, she was noticed by critics in a sparkling performance of Princess Florine, opposite the Bluebird in act 3 of "The Sleeping Beauty". Promoted to soloist in 1958, she danced her first Swanhilde, the saucy village lass in "Coppélia", and the title character in John Cranko's "Pineapple Poll", set to the merry tunes of Arthur Sullivan. She had notable success in both parts, as "her small, light frame and fleet, sunny style made her a natural soubrette." Named a principal dancer in 1962, she subsequently danced all the ballerina roles in the classical repertory.