Complex sentence: Collier was a drama coach for many famous actors, including Audrey Hepburn, Vivien Leigh, Marilyn Monroe, and coaching Katharine Hepburn during Hepburn's world tour performing Shakespeare in the' 50s.
Split into simpler sentences: Collier was a drama coach for many famous actors, including Audrey Hepburn, Vivien Leigh and Marilyn Monroe. She also coached Katharine Hepburn during Hepburn's world tour performing Shakespeare in the' 50s.