Simplify the following text for a Grade 8 native English-speaking person.
Original: In 1955 , she sang the part of the Marschallin in Der Rosenkavalier for the first time ; it was in a series of performances to celebrate the opening of the restored Vienna State Opera House .
Simplified: When the Vienna State Opera House was restored in 1955 there was a special performance of Der Rosenkavalier .