Obviously anything concerning this "Pony Posse" gets my attention! I still grin at the mere mention of it.
Cinny, you are within your rights to inquire about the blocked usage of the arena. You are a paying customer, and not getting a reduced board fee for this inconvenience. Simply state what you did in your post. Perhaps there is a set time for the PP to use the arena. If not, maybe because of your inquiry and concern about your loss of time and training with your horse, there will be a set time.
Please keep us informed on how this plays out, and (I realize this is kinda sick on my part) any further developments concerning the Pony Posse.
Be the kind of woman that when your feet hit the floor each morning the devil says, "Oh crap, she's up!".