In 1969, Guy was selected as one of fifteen soloists to sing at the Investiture of the Prince of Wales and later joined the Opern- und Schauspielhaus Frankfurt in 1972.
[3] While at the school, she earned praise from The Times's music critic for her account of the aria "Inflammatus" from Antonín Dvořák's orchestra Stabat Mater in December 1954.
[4] Guy was awarded the Mary Cantell Oratorio Scholarship, the Hendon Music Prize and the triannual Worshipful Company of Musicians Silver Cup.
[2] Guy made her debut as a mezzo-soprano singer at Sadler's Wells Theatre as Dryade in Ariadne auf Naxos.
Guy received praise for her performance and one critic noted "the assurance with which [she] projected her resonant contralto tone … was irresistible".
That same year, she played Flosshilde in Hans Hotter's production of Götterdämmerung at Covent Garden with fellow sopranos Rita Hunter and Birgit Nilsson and conducted by Georg Solti.
[3] Guy joined the Opern- und Schauspielhaus Frankfurt in 1972 and five years later acted as the Countess in the Welsh National Opera's performance of The Queen of Spades with David Lloyd-Jones serving as conductor.
[1] She and her husband Mitchinson frequently performed at the Three Choirs Festival, where she played the Angel in Edward Elgar's The Dream of Gerontius in 1977 at Gloucester.