I don't like the sound of your instructor.. I would be looking for someone different.
I've noticed that when you take lessons from people versus when you have your own horse and take lessons.. they are much different. When I used to take lessons, everyone never bothered to explain things, just told me to do whatever and yell at me when I got worked up. Now that I have my own horse, the instructors go out on a limb to help me and explain things because they know I will fire them if they aren't being respectful or not caring enough to make sure I understand the mechanics behind every tap or why I play with the reins or why my horse does this or that. They work WITH me.
You need to stand up to this instructor. Tell her you have a lot of gaps that need filling with answers and explanations. You need to know WHY you do things, and if you don't agree with them, tell her. If she yells at you, calmly tell her that you are trying to learn, and if you aren't learning then you will find someone that is willing to TEACH, not tell, you.
You are paying for these lessons, and if you don't even have a good instructor that can help you figure things out, then you are wasting your energy and quite frankly, your money too.
The lesson horses come with the territory. Once you get a better handle on what to do and WHY, then they will start giving you more respect instead of a hard time. But I think the main issue you are having is communication issues with your instructor.. maybe even a teaching method clash.
Something I tell myself when I'm looking for a good instructor:
"They need to work well with ME AND MY HORSE"
Since you are using lesson horses:
"They need to have a learning style that works well with me"
I hope it only takes a conversation to turn your lessons around :)
Have you tried talking to your instructor at the end of lessons about why you did things, etc?