Della Casa sang the part of Zdenka in the performance of Richard Strauss 's Arabella at Zurich Municipal Opera House to her revered soprano Maria Cebotari 's Arabella in 1946 .
In 1946 Della Casa sang the part of Zdenka in Richard Strauss 's opera Arabella in Zürich , and again the following year when she sang for the first time at the Salzburg Festival where she was to sing many times during her career .