Spoiler: don't read this post if you didn't watch the movie.
So we see that Elizabeth and Sue do not share the same consciousness because they have no memories of what the other does when one of them is asleep and the other awake. Sue seems to be a clone of Elizabeth but with her own mind and memory. But if they're separate beings, why does Sue die after killing Elizabeth?
Yes, they are one as is repeatedly stated during the movie.
shareOk, but if they're one, why don't they have recollection of the actions of each other?
shareWho says they don't?
shareif they share the same mind, why is sue so surprised when she wakes up to the food all over the walls?
why is elizabeth so surprised to find sue on late night TV calling her jurassic?
i think at first they shared the same consciousness, but just like multiple personality disorder or mkultra soldiers, eventually there was a split in the mind, and one side was compartmentalized from the other.
and, of course, near the end with the "monster", the personalities merged again
I think you gotta supply your own logic to this one.
We clearly see that when one is active, the other is in a comatose state. Thus, it makes the most sense that they can't be aware of what the other is doing.
You could easily read it as something something "you are your own worst enemy" especially as it relates to women and beauty standards. You could also say "women are always pit against each other, even direct clones" lol. I'm not saying these are great explanations, but it gets your wheels turning. I do agree with you that it's weird that older Demi feels so upset when she sees her Substance self, to the point that she chooses self-sabotage but again... maybe the point here.
Why do they seem to not have recollections of each other's actions even though they're still one, and share the same mind? I guess my simplistic answer is, the same reason they can even have separate bodies at all, and hate each other, even though they're still one.
If you're going to symbolize inner conflict and self loathing via two separate characters, might as well make it look like one looking at the other and saying "what has she done?!", rather than one looking in the mirror and saying "what have I done?!".
Did they really not remember each other's actions, or are they simply regretful of each other's actions, and presented it as surprised and angry? I can't remember after one viewing.
This is a pretty deep thinking movie, so even I'm not sure I gave a wholly good answer.