Im going to say that this movie is "hands down" one of the most confusing movies I've ever seen.
I can't tell if the main character Diane was having a dream, fantasy, disillusions. The only other movie that has made me think so much is Persona, a 1960's movie whose plot was similar.
Since the main character in Persona was having double personality illusions, I'm going to think the same for Mullohand dr.
My final opinion of the plot is that Diane used to be in the movie business but she wasn't a good actress. So she made up this whole fantasy about being a good actress etc.. and in her fantasy she involved characters from the movie industry like Camilla, the director, the directors mother, the cowboy.
The fantasy was going good until she started becoming lost in it and couldn't figure out which one was her real character, Diane the real her or Betty (her fantasy's personality)
I think the fantasy started to go bad at one point and the voices of her made up characters started to disturb her everyday life, so she just killed herself.
That's what I thought of the plot, simply as a fantasy gone wrong.
What theories did you guys come up with?