OOOOO a show in edmonton does this every year, I wanted to, but we never go to the show :(
BUT! I have some ideas.... borrow a pink browband for your horses bridle, and there is hoof polish you can buy with sparkles in it... you could even do silver or something, because im not sure they have pink. BUT BE CAREFUL! DO NOT do the hoof sparkle (its called twinkle toes) unless this is the last class of the SHOW. It does NOT come off (unless you literally sand it off!) and it is illegal in the show and you could be diqualified.
And there is sparkly gel you can get at almost any tack shop to put on your horse. And maybe you could get a pink (or make) a helmet cover? :) I want pictures! Lol good luck!
If there are no horses in heaven... im not going.