Yep, "Hide Your Hiney" is a Parelli thing
Anyway, you need to figure out WHY she is running over you. Horses will run into people for 2 reasons. One, they are trying to dominate you, or two, because they are UNCONFIDENT. If you think about it, in a herd of horses, where is the SAFEST place to be when a predator is near? In the MIDDLE of the herd! Horses will crowd people when they feel unconfident because they have safey issues.
So, when you are working her pay close attention to her body language. Is she relaxed, soft and suple? Or does her body seem tense, her eyes not blinking, can't bend on a circle, looks to the outside, seems stiff in the shoulder, etc. If you decide that it's a dominance thing with her, by all means block your space. Use the stick, your arms, something that's going to let her know that she can't barge into your space. If you decide it's an unconfidence issue, you have a lot of work to do to gain her trust to where she won't crowd you. If you discipline a horse that is crowding you because he is UNCONFIDENT, you will never fix the problem.