Years ago we had bought a young brood mare that didn't like bathes. She would set back and flip herself over. So here is what we did and she doesn't mind them at all now. With horses that are really scared I don't like to tie them as it creates a whole other set of problems, let alone run the risk of hurting or killing herself. Use a round pen, outdoor stall, or a run on a stall. The biggest thing is to make sure you can reach the whole pen with the hose. I have a nozzle that has a gentle shower that I use attached to my 100 foot hose in a 30-40 foot round pen. I stand in the middle with them on an 8ft cotton lead and let them run around me in a circle, almost like they are lunging around me and I keep spraying them until they settle down even a little then I would give her a break, and then start again. It they are to much to handle on the line then turn them loose in the pen and spay up over them and let it fall down like rain, that is how I do it when they are on the line also. That's why you get a little wet so pick a warm day.

When she would settle down even a little at first go from a run to a trot we would stop for the day and pick it up the next time and I would ask for a little more each time. Good thing is we have hot summers that start early so it makes it easy.

Hope this helps