Complex sentence: She was one of the first women writers to become a contract worker at Warner Brothers, where she worked from 1943-1948 and is best known for The Man I Love (1947) and Mildred Pierce, although uncredited for the latter.
Split into simpler sentences: She was one of the first women writers to become a contract worker at Warner Brothers, where she worked from 1943-1948. She is probably best known for The Man I Love (1947) and Mildred Pierce, although uncredited for the latter.