maybe put he hose on and just water it on your hand then rub that water on her and keep doing it a couple of times then maybe try and put it on her but if she still doesn't like it just go to a sponge
I would start out using a sponge
Try using a sponge rather than hose as it is less scarier for a horse and they'll think that the sponge is just a brush
Pressure and release. Warwick Schiller did a great video showing the concept in relation to getting a horse to allow its head to be washed, the same concept applies but as Bree said, start at the hooves and work up.
hey try turning the water pressure down and starting from her hooves and gradually work your way up her body. also maybe teaching her to stand on the ground might be helpful.