I just found this anonymous post on Data Lounge:
I seem to recall a pre-Mommie Dearest interview with Bette, where she slammed Faye for being completely unprofessional on the set of "The Disappearance of Aimee." In either the same interview or a different one, she praised Joan for always being professional despite their on set clashes. Bette, I believe, had more respect for Joan than for Faye and would've happily worked again with the former than the latter. The only thing necessary for the triumph of evil is for good (wo)men to do nothing.
James Woods, who co-starred with Bette and Faye on "Aimee," singled out Faye in a 1979 People magazine interview as the most unpleasant person he had ever worked with.