[cheebacheeba]

My take:
I'm gonna go with "she created that character and story in her mind"...all the scenes featuring the guy, the truck included, was her creating a "villain" so as to further seperate her two ?personalities?.
So while some scenes featured "her as the bad guy as her etc", some were just playing out in her head to further reinforce the personality to herself.
The truck didn't exist. The female headless victim didn't exist.
The crash was just her crashing, perhaps her other personality PUSHING to put them in a situation where she could dispose of her friend.
Notice how though, she only created situations and events for this "bad guy"?
No back story, no name, no reason for being?
This pretty much fits in with it if you ask me...there was no history, as it was just her all along, no reasons, as she was simply fucked in the head.

I'm not sure what other plot holes there were...have not seen it in some time.