I am sorry you are going thru this. It sounds like you know better.. and a horse that is not trained is not "stupid" he is ignorant.. and ignorance means not knowing. No horse was born knowing what we want when we train it.
It sounds like you are young and have been taught to be respectful of your elders and this trainer is someone you do not want to stand up to (or are not allowed to stand up to).
Here is what I suggest. When she tells you do to something that you know is going to be destructive to your horse, just don't do it. Let her yell at YOU (it is noise.. she is not beating you.. and yes, it is hard to hear). Meanwhile, while the trainer is yelling at YOU, the horse is not being abused or hauled about in a manner you know is wrong.
I do not know if you are paying for this trainer and barn, but if you are, you can remember this. The horse is YOUR horse. You and your family bought the horse, you pay the board, you pay the vet, you pay the farrier, you pay for the equipment. The horse is YOUR property and no one has a right to tell you to abuse your property.
Good luck. Again, I am sorry you are in this fix. Just remember two things. First is that yelling is mostly loud and air. You can choose to ignore it. Second is the horse is your property and you can choose to do as told or act ignorant and listen to all the noise from your trainer while not acting on it.
Good luck. Do you have pictures of your horse? Is that him in your Avatar? :)
There is something about the outside of a horse that is good for the inside of a man. ~Winston Churchill
) Dinosaur Horse Trainer