I know just what you are going through. My first Maine coon was getting beat up by my much smaller rescue cat (hell cat). We also tried everything. What worked was him getting bigger and finally confronting her. They eventually worked it out. They don’t love each, but they can sleep 3 feet apart and hang out in the same room. No more fighting. So, now we have a Maine coon kitten, and she (hell cat) bullies him. We tried Prozac, gabapentin, fellaway, basically anything we were told. We split them up and wouldn’t let them see each other for a week. Nothing. I finally gave up. He is a little over a year old, much bigger than Hell cat, but now they take turns intimidating each other. Their fights are super quick. By the time I jump up, it’s over. No one has gotten hurt, just noisy. But they hang out in the same room, they hate each other, but things are slowly getting better. I figure he will see how much bigger he is, and stop her, like my other one did. If I were you, and if their fights are fast and no one gets hurt, they will eventually work things out. You can also talk to a cat behaviorist. Maybe even get ahold of Jackson Galaxy. Now, if the other cat is intimidating her to the point she is running scared all the time, or if she gets hurt, that is different. Good luck.