In 1947 and 1948 , Schwarzkopf appeared on tour with the Vienna State Opera at London 's Royal Opera House at Covent Garden on 16 September 1947 as Donna Elvira in Mozart 's Don Giovanni and at La Scala on 28 December 1948 , as the Countess in Mozart 's The Marriage of Figaro , which became one of her signature roles .
In 1947 and 1948 , Schwarzkopf appeared on tour with the Vienna State Opera at London 's Royal Opera House at Covent Garden on 16 September 1947 as Donna Elvira in Mozart 's Don Giovanni and at La Scala on 28 December 1948 , as the Countess in Mozart 's The Marriage of Figaro , which became one of her most famous roles .