I hate to say it, but I think that Anebel's point is valid. Usually, if you are fighting a horse a lot, the horse is trying to tell you something. It might not mean that the horse can have what it "wants", but it has a problem somewhere and it's trying to tell you that.
It can be your way of riding it, or bad fitting tack or other issues.
Have someone else ride her, who has a lot more experience and see if that tells you anything. It can be a bit dismaying to see a horse that you struggle to ride become like butter in the hands of anotehr , better , rider. But, you might learn something. I have had this experience, too.