Complex sentence: Instead, Marguerite Long--who was known for her performances of the works of Gabriel Fauré and Claude Debussy and had earlier asked Ravel for a new work, later debuted the concerto.
Split into simpler sentences: Instead, Marguerite Long--who was known for her performances of the works of Gabriel Fauré and Claude Debussy. She had asked Ravel for a new work, and later debuted the concerto.