On the ground, prod your horses side where your legs would touch her when your riding. As soon as she pivots on her hind and
crosses her front legs over, release her and pet her neck.
Pet don't
pat because patting is actually a negative sign to a horse, while the stroking of the fur is a calming sensation.
And make sure it's
prodding because a series of prods are more irritating than a constant pressure, and make the horse think "Hmm...maybe I should move away from this pressure."
If there isn't a response, prod harder and harder until they move. That teaches them that if they move over on the light touch they won't have to deal with hard prodding later.
Basically the same for the forhand turn, but on the haunches instead.
As they begin to respond more willingly, ask for more steps. Soon you'll be pivoting all over the place. It's always worked for me in the past
Good luck, let me know how it goes ^^