Start with the basics - does she bend and counterbend each direction? Can you circleher on a true bend and a counterflex?
Here are some grea bending exercises (fresh in my memory, this is what Maia and I are working on!)
1) Circle to the right 20m, true flexion, when you reach X, do a 10m circle, then do another 20m circle to the right in true flexion. When you reach X again, ride as straight a center as you can, then switch bends and circle true flexion to the left. Do a 20m circle to the left, then at X circle to the left for a 10m circle, then do another 20m to the left - then switch back to the right.
Once both of you have gotten a hang of this exercise at a walk, do it at a trot.
Once you are comfortable with true flexion both directions, make one of the 20m circles a counterbending circle.
2) Do 10m circles at each of the major dressage ring letters (a, c, m, b, f, h, e, k) and the straight lines in between in true flexion. Once she is comfortable with this, ask her to counterbend the straight lines, and do true flexion through the circles.
Once she is okay with the counterbending on the straight lines, then add a 20-m counterbend circle at both C and A instead of true flexion 10m circles.
3) Do counterbending leg-yields along the wall, making a 40 degree angle to the wall.
4) Do counterbending loops - from K to X, bend the horse to the left and leg yield across. Then from X to H, bend to the right and leg-yield to H. Repeat on the other side.
5) Start a 20m circle on true bend, then spiral down to the middle to do a 10m circle, then counterbend that 10m circle for a couple rounds, then leg-yield back to the 20m circle. Keep the counterbend for a half circle, then ask the horse to true bend again.
6) Start a serpentine, and switch flexion (always remaining on true flexion) for each loop. Make an S-shape in the middle if you need to to help her through the transition.
Once she is okay with this, then keep ONE flexion through the whole serpentine, so she is counterflexed for half of it. Do this each direction.
Okay, I think I've spewed off enough exercises for now! Let me know if you want more!!