Ballet dancer, Choreographer. She was a South African ballet dancer known for her roles with George Balanchine and Jerome Robbins at New York City Ballet, and for founding both the Johannesburg City Ballet (later known as the PACT Ballet) in South Africa and the Westside School of Ballet in Santa Monica, California. She taught many well-known American dancers, including Jock Soto, Andrew Veyette, and Tiler Peck. She studied with Igor Schwezoff in London, touring with the Carl Rosa Opera Company. She also studied with Olga Preobrajenska and Lubov Egorova in Paris, and at the School of American Ballet in New York. In 1939, she joined the Ballet Russe de Monte Carlo, and the following year (1940–41) joined de Basil's Original Ballet Russe, under the stage name "Irina Zarova." Balanchine saw her perform with the Original Ballet Russe in 1940, and created a part for her in Balustrade (1941), a Stravinsky violin concerto. Shortly after, she was touring in Cuba, became stranded when her company disbanded, and worked as a nightclub dancer. After success in this role, she went on tour with her nightclub routine, encountering Balanchine again in 1945 in Mexico City. She then returned to South Africa, leading her own company, before joining the New York City Ballet in 1948/49, where she stayed until 1958. After becoming a soloist after only a year at the City Ballet, she danced in leading roles or created roles in numerous ballets with Jerome Robbins, George Balanchine, and others. She was regarded as the "classic interpreter" of the role of the Siren in Balanchine's The Prodigal Son, after studying with Felia Doubrovska who originated the role. A 1953 review in the New York Times noted that "[Mounsey] dances it with a studied voluptuousness that makes it mockingly cold." She retired from NYCB in 1958 and returned to South Africa where, with Faith de Villiers, she co-founded the Johannesburg City Ballet (later named the Performing Arts Council of the Transvaal, or PACT Ballet). In the 1966 she settled in Los Angeles, and took over "Academy West" in 1967 with Rosemary Valaire, a close friend and collaborator. The two later moved the school to Santa Monica, renaming it the Westwide School of Ballet. She taught in "neoclassical Balanchine technique", and her students included Jock Soto, Andrew Veyette, Tiler Peck and Joy Womack.