Simplify the following text for a Grade 8 native English-speaking person.
Original: In 1949 , she made her debut at La Scala Opera House in Milan as Sophie in Richard Strauss 's Der Rosenkavalier and Marcelline in Beethoven 's Fidelio .
Simplified: In 1949 , she sang at La Scala Opera House in Milan as Sophie in Richard Strauss 's Der Rosenkavalier and Marcelline in Beethoven 's Fidelio .