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 :)
There are a bunch of exercises you can do, but counter arc circles are good to start with:
Put horse on a circle at the trot. When you close the circle ride the horse in the opposite direction, (figure eight, but holding the same body position. This is hard work, so release on one correct step going back to the original direction/same as bend and build until the horse can hold the counter bend around the second circle.
Keep the circles large at first as that is easier for the horse. As the horse becomes better, when you put them on the counter bend and spiral down. If at any point in the spiral the horse seems to struggle, let him go on the original circle/same as bend.
When the horse can spiral all the way down on a reverse arc and settles into the spin, hold for only as long as the horse can and then come back out on original circle/same as bend. When the horse can hold one turn with the counter bend, with each new turn start bringing head straight and then into direction of the turn. Then take horse out on circle with new correct bend.
Keep the trot going and if the horse breaks to the walk or stops you asked for too much too soon. Drive him out and start again. Important to keep forward movement and maintain cadence.
Man, did you want to do a dressage style turn on the haunches?
Sorry, if you want a dressage turn on haunches, you do not want the horse to stop the hind end. You need to work on connections with the shoulders both into and away from the rein, then spiral down on correct bend and drive out before the hind end locks in. In fact, I would also work on driving the hip in with the outside leg keeping shoulders and hips moving forward and into direction of the pivot then ask the shoulders to move around the hip without stopping the hip. Starting with one step and building as above.
If you want a western pleasure turn on hind for reversing directions you again need control of the shoulders both into and away from the rein. You will also work on the inside foot falling under your stirrup/foot so it is out of the way for the outside leg to come across. You can get this by asking the horse to follow the leading rein and when he does not, disengage the hip until that leg on the leading rein flies under your foot then release the rein and continue until the horse will put the foot in the correct place without going to the hip. The outside rein asks the outside shoulder to follow.