Keep her feet busy, keep her mind active. My stockhorse will bite, snake his neck etc. at cattle if he is bored/still, but when he is working, he gets on with his job and isn't aggressive. I would take a break from cutting for a while, and just work on moving cattle from one point to another, driving in different directions, run the cow for a few strides then come up to the eye and turn it, drop back and let it walk, etc. Make her work hard! Cutting leaves it up to the horse a lot more, which is a perfect opportunity for her to get aggresive. Give her more guidance and directions, and she may settle down to her job and stop the aggressive behaviour.
Just a suggestion, works with my boy :]