Allow me to say something here if you will. Western and dressage are two separate ball games. One encourages less movement of the hands, and light movements of the legs, more muscle-horse communication, rather than western, reins-bit, and direct leg movement; if the horse is trained in the 'normal' fashion. But that's a bit besides the point.
What I'm trying to say is. I don't think she's trying to be too careful. I think that Barney is honestly confused with what he should be doing, and that Connie doesn't know how
he was trained, thus is only doing what she knows to try and figure him out. He's probably just a very sensitive horse, and very responsive to movements of any sort. I hate to go off a breed, but I can say from past experience that Arabians are
very sensitive horses and react to things very very quickly and well.
Not every horse is trained the same way either, you have to keep that in mind. Let alone, a horse professional won't always know everything about every discipline of riding. Susan made it very clear that she knows Western and basics in english. Yes, you might say that dressage is the basics for all of riding, doesn't mean that all the cues are just simple to explain and figure out, if that was so, everyone would be doing it!
Honestly though, if a horse started to piaffe while I was sitting on them, I would be confused too. I would start thinking, as Connie probably is, 'ok, what did I do? where are my legs placed? what are my hands doing?' if anything becoming MORE aware of what I am doing with myself when this happened.