Shelley made her Broadway debut as Gwendolyn Pigeon in the original 1965 production of "The Odd Couple" (starring Art Carney and Walter Matthau). She reprised the role for the 1968 film version (with Jack Lemmon replacing Carney), and the first season of the subsequent television series (starring Tony Randall and Jack Klugman). She and Monica Evans, who co-starred as her sister Cecily Pigeon, were the only two performers to appear in the original play "The Odd Couple" and both the film and original television adaptation—and in the same roles.