Well, if she was a wall, I would say use a dark stain to faux finish her and she would be FABULOUS and people would line up to have you do their wall/horse.
All kidding aside, I have only body clipped one horse and had a blast but it wasn't with a show coming up in 4 weeks. I know that KaThim's body grew out pretty darn fast after I body clipped him this spring (he is the barn owners horse) and you couldn't tell he'd been clipped. Wait til a week before the show and get a pro out to clean him up and see what you have after that.
It isn't the end of the world - it is hair and thank God hair grows back!