Pearlsacarolsinger
Up in the clouds
That's great, but be very careful not to proceed with anything until that money is back with the original buyer. Not even a viewing. I'm sure you will be (especially after this), but this horse currently doesn't belong to you! He sounds amazing and I'd certainly be tempted if I was looking!
Please do take legal advice about how to proceed, OP, although ,as you gave the buyer every opportunity to collect the horse and she hasn't paid you to keep him over the last week, I would expect you to be fine to readvertise and sell on.