Complex sentence: In 1933, she directed her choir in the Broadway production of Virgil Thomson and Gertrude Stein's opera, "Four Saints in Three Acts" and in 1935, she was the choral director chosen by George Gershwin for "Porgy and Bess".
Split into simpler sentences: In 1933, she was in a production of "Four Saints in Three Acts" by Thomson. In 1935, she was the choral director chosen by George Gershwin for "Porgy and Bess".