 When Maria Callas cancelled her appearances in three out of the four scheduled performances, Collier stepped in, to great acclaim.In 1967, she created the role of Christine Mannon in the world premiere of Marvin David Levy's "Mourning Becomes Electra" at the Metropolitan Opera, in which Evelyn Lear and Sherrill Milnes also sang.Her other roles with the Met included Musetta, Tosca (on tour), and Santuzza in "Cavalleria rusticana".