Of course, we only lope at our own cattle. We know them well enough, since we only have about 70 head, to be able to apply the correct amount of pressure. We don't get vocal, because you see enough people at sorting shows hooping and hollering like a bunch of monkeys, and it seems to only make things harder for them. All the cows can hear them yelling, so they all get pumped up, not just the one they are targeting. We go in quiet and use our horses to work them. Now, well placed whistling I can understand.
I'm not sure if an interest in cows is built up over time, or bred. I think certain horses learn to go through the work, but good cow horses will be aggressive towards a cow, like ear pinning. I've seen a few Arabs with some cow sense, but granted they are far and few between. I think the fact she was so calm is a great thing. Plenty horses are terrified of cows. Don't want anywhere near them. Those are the ones that are fun to train when their owners want them to sort or cut.
A kick at a nip is pretty understandable. :)