Diener started out on Broadway in an unsuccessful revue, Small Wonder (1948), and in 1950 was briefly in the play Season In The Sun. Her effective singing style and attractive physical appearance marked her out for future popularity although only twice would she find roles in box-office hits. She was married to Albert Marre, and their first collaboration as director and star came when she appeared in Robert Wright and George Forrest’s Kismet, which opened on Broadway in December 1953. Marre chose her for the role of Lalume and it was thus that she introduced ‘Not Since Ninevah’. Her co-star was Alfred Drake, with whom she sang the duet ‘Rahadlakum’. In 1955, Diener played in the London production of Kismet, reprising her role. Back in the USA, she was cast in Wright and Forrest’s Grand Hotel but the show did not make it into town; a new version finally arrived on Broadway in 1992.

It was some years before Diener had another leading role in a successful New York show. This came when she played Aldonza in Man Of La Mancha (1965), by Mitch Leigh and Joe Darion. In this initially off-Broadway show, also directed by Marre, she played opposite Richard Kiley and their performances were a significant factor in the show’s subsequent and unexpected success. Diener returned to London with this show and also appeared in a Paris production, starring opposite Jacques Brel.

In the 70s Diener performed in unsuccessful shows; Cry For Us All (1970, with Paul Muni), and Home Sweet Homer (1976). In semi-retirement for some years after this, Diener made an impressive if brief return to Broadway in 1992. This was for the revival of Man Of La Mancha when she again sang the role of Aldonza, taking over from Sheena Easton in April and staying until the show closed in July, and vividly demonstrating to audiences that neither her singing ability nor her stage presence had deserted her.