Desensitizing the "Quirky" Horse

a few times before I ever ask her to put a foot in the trailer or on the ramp. I take my time. Withdraw the clippers before the horse decides to withdraw her head. Aim the hose first beside the horse then away then move it up just to the point of hesitancy perhaps a hoof then away and so on. 
Knowing when to withdraw requires good timing and the ability to read a horse.
Every time we let horses express their flight response by bucking on the lunge line spooking to the centre of the arena or tetherballing around us to avoid the spray bottle we confirm their fear rather than habituate them to it. Allowing your horse to rush the approach to the jump and away again on the landing side confirms your horses fear that jumping is a scary process indeed.
You dont want to trigger an adrenaline spike by moving up the scale too quickly. Dont ask for anything that you may not be able to contain and dont let the horses legs flee. Try to minimize the escape distance. This may involve sending the horse to training camp with a professional who specializes in breaking young horses thoroughly.