[1] Initially Sibley had small roles such as a friend of Swanhilda in Coppélia and Red Riding Hood in Sleeping Beauty.
During 1959 Sibley had the chance to be tutored by one of the greatest ballerinas of the twentieth century, Tamara Karsavina.
[3] Karsavina said to Sibley, "To get the full benefit from battements frappés we must train our muscles to give a quick reaction.
"[3] On 24 October 1959, Sibley was unexpectedly allowed to dance the leading role in Swan Lake partnered by the principal dancer, Michael Somes.
"[4] One of Sibley's first important roles was in Jabez and the Devil (1961), choreographed by Alfred Rodrigues, who was among the earliest to recognize her talents.
Further roles were in Ashton's ballets, Symphonic Variations and Daphnis and Chloe, Jerome Robbins's Dances at a Gathering and Afternoon of a Faun.
Among the other ballets in which Sibley created roles are Monotones, Jazz Calendar, Anastasia, Triad, L’invitation au voyage, Varii Capricci, Fleeting Figures and Enigma Variations.
After their divorce, in 1974 she married London-based banker, (Richard) Panton Corbett, of a landed gentry family of Longnor, Shropshire, who changed their name from Plymley in 1804 to inherit the estate from their relatives, the Corbet baronets.