The exercise that I think is going to help you understand the bending aids is to do a turn on the forehand. Start by doing one yielding the haunches to the left (this will be your easy way). At a halt, flex the horse's nose to the right just slightly (enough that you can see the inside eye). Then using your right leg, move the horse's haunches to the left, but keep the right flexion. Use your left leg and rein to tell the horse to only take one small step sideways with the hind legs. Using this combination of aids is almost the same as a bending aid. Now try it to your difficult side. Flex left, use your left leg to push the horse's haunches over and your right leg and rein to tell her only to go a little bit, and make sure she stays flexed left.
If she starts backing up - immediately go forward. You can also do this in a spiral in/spiral out exercise. Ride on a small circle in the middle of the arena and yield the horse out to a big circle (same combination of aids).
Yields are the best way to learn about bending aids - and if you lose the bending aid then go back to a yield. You can also do this for transitions to help them be smoother - do a transition in the middle of a yield (upward or downward). Good luck!
They say money doesn't buy happiness -- well happiness doesn't buy horses!