I agree with Speed Racer.
At my camp there's a little pony mare that will stand there and pin her ears like crazy. She does bite/kick at people she sees as easily intimidated but she won't bite or kick you as long as she feels like you're in charge. It's just her personality. She's just a very business-like mare and she doesn't like not working, therefore she lets you know with her ears. I actually prefer that she pins her ears so much. I've been around horses that gave no warning, they'd just kick/bite out of nowhere, that's scary. But with pissy horses you can see where they're coming from WAY before they do anything about it, so you can protect yourself, if necessary, before you're "in danger." :)
I wouldn't worry about it unless she actually starts biting/kicking (I think we've covered what to do if she does start biting/kicking). I mean, I might not let little kids around her just because they can't get out of the way quickly enough if she decides they're wusses, but other than that I wouldn't worry.