You poor thing.
This sounds just awful.
Is it possible that she has an allergy and it is making her feel really bad? Has she always not slept during the day? Has she always been a screamer (there is nothing worse than a screaming child...it makes me angry too). It may be worthwhile trying an elimination diet to see if there is somehing upsetting her system. It sounds a bit like she is in pain with the thrashing and screaming etc.
I don't really have any other advice, I have always had a little nap time routine for Flynn and we generally don't have any problems.
I hope you figure it out soon, you really need a break
