My horse does this at first when I give her baths, the best advice I can give you is to find a point that she is most comfortable with the water being sprayed on her. For instance, my horse doesn't mind her feet being sprayed. Start there and work until your horse is comfortable and slowly move around her body. If she gets nervous or jumpy, move back to her comfort zone and she should eventually calm down.
Not sure where you are in the country/world but I am guessing if she stood fine last year and is dancing like crazy during this hosing it was because of how cold the water is. Water coming out of the ground (be it ground water or piped water) in the northern states is approximately 40deg this time of year. That would feel pretty darn cold even if she was hot to start with.