I would probably skip these shows. I also have some anxiety issues and just reading your post made me feel a little sick. Agree with the previous poster who pointed out that any little slip up on you or your horse’s part will be magnified in your mind and blown way out of proportion. Combine that with a snide comment or nasty look from the old BO and you may set yourself up for an unpleasant memory, which could have a negative long term effect on you and your future shows. Also, as someone else said, why support this person with your money? Go spend your money at a show where you can walk around relaxed and really enjoy yourself with your horse.
PS: I am a real whimp when it comes to confrontation, real or perceived.