Complex sentence: Her daughter Nargis was first cast in a film by her mother at age 6, and went on to become a major star in the 1940s and 1950s.
Split into simpler sentences: Her daughter Nargis began her film career at age 6 when cast by her mother in one of her films. Nargis went on to become a major star in the 1940s and 1950s.