I know how badly you both must feel. I know you have tried everything and have been very good to her.
I think she really needs to be in a one cat household. I have owned two Main Coons in my life and both of them had pissing problems if there were other cats involved. They seem to me to be more territorial than other cats.
I will put out the word.
On another note...we are trying to find Tybolt a home....Naomi is not going to be able to keep him. *sigh* He is such a sweet cat and he has gone through so much. I hope we find him a good home soon.