lots of patience and hours of trying to work it out of her...
i've had a couple over the years that were like that...one would kick at "things" so i took about 15 empty 2 liter plastic pop bottles and laid them all throughout her stall, it kinda freaked her out at first, every time she would walk, one would move or get in her "zone" and she would kick...but she eventually got tired and quit....then everytime i would go in to clean out the stall, i would gently toss them close to her back legs with a pitchfork...she would kick at that too, but eventually she would get tired and just quit...everyday she would do it a little less...about a week later, she was over it...
ive done the broom method too...but the thing ive noticed with it is you have to continue to do it until they stop....dont just brush her leg with a broom and when she kicks stop for the day...their kicking is their way of saying go away....so if you stop when they kick, they have won....and thats generally why they continue doing it....you have to keep doing it until she stops kicking...it may take an hour, maybe two! ...but she will eventually stop...and do it every day, even a couple times a day...it should get to the point where the time it takes her to stop kicking gets less and less and eventually they will just stop...
you've mentioned her kicking at the showstick and washing....first is the tip of your showstick too sharp???? sometimes that can cause them to kick...if its not...then just keep working her with the stick until she stops...when she stops kicking, then the "lesson" is over...same for washing...spray her legs with the water hose...keep spraying them until she stops kicking...these things generally just take patience and time...