Very often horses don't do what we want them to do because we don't know how to properly ask them. : ) It does sound like the horse you are riding might have a program of challenging tender-foots. Does your instructor have another horse you can ride until you learn the cues? If not, just stick with it and try to keep your frustration level low. If you get upset that will transfer to the horse and then it becomes more work for both of you.
Also, your instructor will move you to an English saddle when she feels you are ready. Riding isn't just about being able to sit up there and go around looking good. It's about learning skills that allow you to communicate with a horse and this takes years, not just a few lessons. It is never just about the rider but about the horse and rider as a team. And it's a wonderful adventure.
If you ever find yourself in a fair fight, it's because your tactics suck. ~ Marine 1SGT J. Reifinger