I think that a part of her pissy look is fron her wanting to go where she wants to go and at her speed. And the gets frustrated when Im asking her to go where im telling her at the speed I want her at. Why do I think this? Because when im done w/t practice on barrels and go to ride a few big circles around my whole riding area, she wants to turn every barrel she gets close to because that is just what we were working on, so she pins her ears, swishes her tail, has a little mare fit until she finds out I just want her to walk in a straight line. I guess its just her own little way of dealing with frustration/"I dun wanna" syndrome.
As for the ors exercise, I do what Wares said almost every ride if I have time. It helps me determine what kind of day its going to be lol. On a good day, she will give to both sides with no circling for one or two steps. On a bad day, she is distracted and circles several times before giving.
And have you tried giving her a task that will stimulate her mentally? Like say maybe even something like doing figure 8's or serpentines and stopping briefly in the middle occasionally