 She also appeared as a freelance artist with the Oper Frankfurt, the Hamburg State Opera, the Cologne Opera, the Bavarian State Opera, Deutsche Oper Berlin, and the Vienna State Opera during the 1960s and 1970s.In the mid 1960s Żylis-Gara began to become a major presence on the international stage, beginning in 1965 with her debut at the Glyndebourne Festival as Octavian in "Der Rosenkavalier".She later returned to that festival in 1967 to sing Donna Elvira in Mozart's "Don Giovanni".