I think having your instructor ride your horse for you a time or two would be good, but only if you are there to watch how she handles the spook, if it happens. YOu want the more experienced person to help you take the steps to getting to the place where you can do it on your own, so you will need to watch and emulate. Perhaps you can ride a calm horse out with her, and she on your horse and see what happens.
It's alwyas true that horses are just absolute masters at feeling the confidence level of their rider and reacting thusly. I know that my horse, Mac, has trouble with spooking when under ME, but almost never under his owner (though I did see him do a magnificent spin with her one time, which she rode out like a champ. Darn, if only I could just BE her!)
Anyway, we are who we are and we cannot just BE confident riders, like snap our fingers and it happens. Especially with a fall and its' aftermath of fear and bad memories. But watching someone else deal with it, and then you litereally pretend to be them, especially when you need to conjur up more assertiveness and it isn't your natural way of being.
Mac is often worried about things on the trail and it is often the same old things. So, desensitziign him to them isn't the ticket. What works is for me to be there to "help" him when he is not sure what to do.
When he stops sometimes to listen, I usually let him , for a brief moment, and then suggest he go on. If he is really super worried, I will let him listen a bit more, but this is really rare now. I mean only when I ask him to go forward and he is so worri9ed that he is about to explode. HOwever, I do NOT allow him to whirl around and try to run away. Having him stand and think about it is one way of working through a worry, but better is to have him move on forward if possible.
If I go past something that is rustling the bushes and he tries to either whirl around and run away or bolt forward, I use one rein to make him turn back toward the scary thing. I don't need him to approach it and sniff it, I just dont' want him to turn his back on it. If he can walk by the scary thing wihtout trying to turn his back on it and run, then that is the best.
I usually keep the outside (farther away from the scary thing) rein on a bit more, lift it upward and put on the outside leg just a bit and focus MY energy past the scary thing but I am ready to stop him is he thinks he can bolt past it. If he did, I woujld quikcly pick up the inside rein (nearest the scary thing) and pull him into a disengagement and disallow him from running away.
If he calms enough to take a big breath and maybe lick his lips, then I turn him away from it in a controlled manner and let him walk away from it.
This is what I was taught, and to be honest, I am sure there are better ways. I would not say this is the best way. It is what I lean on because I am sometimes not able to get Mac to just ignore something and trot on by. That is MY weakness and lack of confidence, I am totally aware of this.