I thought it was a lovely outfit for a freestyle exhibition ride! Elegant indeed!
I'm guessing the bodice part of the outfit was a sort of bustier/corset, which appears to give support. The feather boa might disguse a halter style bra, perhaps?
Agree with the distracting, flopping hair.
Those strapless affairs wouldn't be appropriate for everyone. Like me, for instance. People would pay me NOT to dress like that. One of the first things I thought of was SUNBURN at outdoor shows, especially at our high altitude.
It's a freestyle show in the spring (march), called Spring Carnival. This is a freestyle costume class, everyone is in costume. There are individual classes, quadrille, a artsy performance class, and a pas de deux. This is the pas de deux winnter, with a %75 which includes music choice, costume, equitation, and horse performance.