That's something she would have been taught to do... My neighbor has a Standardbred gelding that was trained by the Amish as a buggy horse, and he does it by instinct now... It's a gate their taught for cart racing too, and if they dont get it right, they're not used as racers...

I have found with the gelding, its something he does when he's asked for a trot, and once you get into the rythem, it's not too bad... I just wasn't expecting it the first time he did it and ended up laughin so hard I almost fell off...

good luck with her...