For all her work with the likes of John Cage, Yoko Ono, and Nam June Paik, it was as booker, presenter and grand impresaria that she made her considerable mark on 20th-century art – especially with New York’s Avant Garde Festival (1963-80). “[She] invented the festival, produced it and coaxed city officials who didn’t know performance art from police procedurals into endorsing it.”