I don't know that this applies to you, but my mare's mare-ish-ness came in the form of being nervous. If she was in heat, she thought the world was out to get her. I put her on straight dried and coarse ground red raspberry leaf (which is exactly what Mare Magic is) and it worked amazingly. Just an ounce a day!
It sounds like you're having a different issue however. But, I guess it never hurts to try.