Simplify the following text for a Grade 11 native English-speaking person.
Original: She also appeared abroad , notably at the Royal Opera House in London in 1951 , as Arline in The Bohemian Girl , and later appeared at the Vienna State Opera , the Salzburg Festival , the Bolshoi in Moscow .
Simplified: Peters also appeared abroad as early as 1951 , when she sang at the Royal Opera House in London , in Balfe 's The Bohemian Girl , conducted by Sir Thomas Beecham . From the mid 1950s onwards , she appeared in several opera houses in Italy , the Vienna State Opera , the Salzburg Festival , and the Bolshoi in Moscow , in 1972 .