The horse knows! Seriously though I'm betting it has to do with her weird ninja costume more than anything.

I had a few horses back when I wore a younger man's boots. Was dating a hottie and took her out to the stables. My mare, who had a gentle disposition, took an immediate dislike to the new gf. Turned out Mama Mare was right. Hottie was hot and a lotta fun, but the hotness was trumped by a far too high maintenance and neediness quotient. Same was true of the horses, come to think of it. Regardless, always defer to your furry friends assessments of others.

A wise old cowboy once told me, "Son, if you have one good woman, one good dog and one good horse in this life, consider yourself a lucky man. Just don't expect all three to come around at once."