Does this horse paw AT you, like a strike, or does she do it at the hitching post all the time, no matter if you are there or not? If she is pawing and pawing and not stopping while tied, then let her stand tied to a tree....battling the branches will take her mind off of it. Time will also be a factor, too.
If she is doing it at you, then take a short crop and give her a short, sharp tap to let her know to KNOCK IT OFF! Its dangerous if they do that, especially if you are right there and trying to pick out there feet. My one gelding is just getting over that. He had had feet issues though, so I always kept that in mind. Is she bored, or has she not had the training? How old is she? Hope this might help. Belive me, I have lost it too before, and in the long run it doesnt pay haha but don't give up.