Agree 100% with amarea's advice - write it down that this is to confirm your & your dad's discussion with the BO on 8/31...and lay out the details that you agreed to. Make 2 originals, have Dad sign both, and have the BO sign your copy (make a sentence that says the BO acknowledges notice was given and received this written confirmation of the notice). If she refuses to sign your copy, make a note right on your copy that you gave her a copy and asked her to sign your copy but she refused - write down the date and time of day that she refused and your dad should sign that note. If there are witnesses to the conversation, it would be great to have them date and sign your note, too, to help prove that she got the written confirmation of your verbal 30 day notice.
The more that you/your dad/your mom/trainer/vet are out there in the next 30 days, the better. That will be a sign to her that she is being WATCHED, and it will make it easier to figure out if there's a new problem emerging. Plus, having the adults observe any problems is powerful - she won't be able to deny it as easily.
Wouldn't hurt to begin to take your personal belongings home from the barn, either...they might just disappear the day before you are to trailer Cricket out of there and she knows you will just 'let it go' because you are so done with this.
Whatever you do, control your temper so that you walk out of there with your integrity and dignity intact - you'll be proud of yourself later that you didn't stoop to her level to fight dirty or talk nasty back to her. It's the better person who can do what's right, and you win when you suceed in doing what you have to do for Cricket's well-being (kind of like being a mom, isn't it?!!). Good luck!