Pony keeps attacking cat?

Recently we got a new barn cat, she's actually one of my cousin's cats that she apparently didn't want anymore. But Binty has been doing a very good job at capturing mice in the barn. And she likes to scale the stall and the frame of the barn to get around or for fun, who knows. Anyways, all the horses let her move as she pleases. Except my pony Nutmeg. She was trying to bite her and has bitten her a couple of times. Not too bad. I was just wondering why though since she's never bitten the other barn cats. She really just doesn't like this one for some reason. Binty is a sweetheart, hasn't attacked any of the horses or anything. What can I do? I'm afraid if Nutmeg goes to bite her Binty with unleash those claws and I don't want to declaw Binty.