Complex sentence: In 1926 Chambré Hardman appointed 17 year old Margaret Mills as his assistant and during the earlier years Margaret would look after the studio in Hardman's absence, mainly when he was in the South of France that year.
Split into simpler sentences: In 1926 Chambré Hardman appointed seventeen year-old Margaret Mills as his assistant. At first, she would look after the studio in Hardman's absence when he was in the South of France that year.