Olive Sarah Gilbert (22 November 1898 – 19 February 1981) was a British singer and actress, who, in a career spanning seven decades, performed first in opera and then in many of Ivor Novello's musicals in London's West End.
After the First World War, Gilbert sang contralto and mezzo-soprano roles with the Carl Rosa Opera Company for more than a decade. She moved into musical theatre in 1935, appearing in Novello's Glamorous Night. She also had roles in his Careless Rapture (1936), Crest of the Wave (1937), The Dancing Years (1939), Arc de Triomphe (1943), Perchance to Dream (1945) and King's Rhapsody (1949).
From 1961 to 1966, she played Sister Margaretta in The Sound of Music, and she appeared as the housekeeper in Man of La Mancha in 1968. She continued to perform into the 1970s.