Start with turning the hose on, and just letting it run near fer feet. Don't try to apply water to her legs until she has somewhat accepted the water going near her. If she dances around, just quietly follow her acting like its not big deal. Don't reprimand her for moving. Then you can start to put the water on their hooves, and again, if they move around try your best to keep the water on its feet. Don't let her moving away take the water away. Once she stops and stands still for a second, then you can remove the water. And then work your way up. Some horses will try and push past you, you are allowed to get after them for that. But otherwise, keep the water on them as their dancing around. If they get too hysterical, you've gone a step too far and you have to back up.
In riding, a horse's energy is like a river- guided by the banks but not stopped by them.