C.O.
it will end when you stop participating in it..
record and document your issues but other than that - stay out of it.
If you can record her stating she will smother him with a pillow - then do - and give it to the police as evidence....
you might have to continue to participate in her drama to get her declared a mental case/mentally incompetent a danger to herself and society - especially with the threats of killing her father....
If she is threatening you and your family - file a restraint order against her.