“[She] epitomized the company’s early eclectic profile by excelling in roles that ranged from Billy the Kid’s Mexican sweetheart to the ‘Bluebird’ pas de deux from The Sleeping Beauty … Because of her lyrical style in ballets like Les Sylphides, Ms. Koesun was often cast as a Romantic ballerina. But she could also show dramatic ferocity, as the evil antiheroine Ate in Antony Tudor’s Undertow.”