The wiki details were interesting - sounds like she was about ready to walk away anyway:
Faye finally accepted the lead role in Fallen Angel (1945). Although designed ostensibly as Faye's vehicle, Zanuck tried to build his new protégée Linda Darnell, ordering many of Faye's scenes cut and those of Darnell's emphasized. When Faye saw a screening of the final cut—with her role reduced by 12 scenes and a song number—she wrote a scathing note to Zanuck, went straight to her car, gave her dressing room keys to the studio gate guard, and drove home, vowing never to return to Fox. Faye was still so popular that thousands of letters were sent to Faye's home and the Fox studios from around the world, begging her to return for another picture. In 1987, she told an interviewer, "When I stopped making pictures, it didn't bother me because there were so many things I hadn't done. I had never learned to run a house. I didn't know how to cook. I didn't know how to shop. So all these things filled all those gaps."
After Fallen Angel, Faye's contract called for her to make two more movies. Zanuck hit back by having her blackballed for breach of contract, effectively ending her film career, although Faye no longer cared to pursue it. Fallen Angel was Faye's last starring film. Zanuck, under public pressure, tried to lure Faye back onto the screen; Faye returned all the scripts.
I have always depended on the kindness of Strangers - and the bastards let me down!