Complex sentence: Boulanger accompanied her ten-year-old sister Nadia to classes at the Paris Conservatoire before she was five, shortly thereafter sitting in on classes on music theory and studying organ with Louis Vierne; she also sang and played piano, violin, cello and harp.
Split into simpler sentences: Boulanger accompanied her ten-year-old sister Nadia to classes at the Paris Conservatoire before she was five, shortly thereafter sitting in on classes on music theory and studying organ with Louis Vierne. She also sang and played piano, violin, cello and harp.