My daughter went back and forth between Mantracker from Science Channel and a rodeo queen. She settled on rodeo queen.
Some ideas some of the other girls have been tossing around...
For a Paint horse, dressing the rider up like an artist, and a drop cloth for a blanket over the saddle pad.
Using a red and white blanket and dressing the rider up as a chef...draping "spaghetti" over the mane.
First date, with a bow tie and formal(ish) gown for the girl.
A hippy, especially if you have a horse with an incredible mane that you could braid up.