Complex sentence: She worked from 1920 to 1921 with Harry Piel in the film series "The Headless Horseman" together, but was increasingly busy in supporting roles and did "The Despisers of Death" (1920), "The Sun of St. Moritz" (1923).
Split into simpler sentences: She worked from 1920 to 1921 with Harry Piel in the film series "The Headless Horseman". She also did many supporting roles and acted in "The Despisers of Death" (1920) and "The Sun of St. Moritz" (1923).