Horse deal gone bad, your advice?

My husband went to look at a colt last weekend. We are not new to horses. He gave the seller a 50% deposit along with a month's board as our truck is currently in the shop so we would not be able to take him home immediately. The seller cashed both checks. Today she called to say that the colt had to be gone by Sunday as she was going on vacation. We told her that there was no way we could get him this weekend and as far as we were concerned we had until 20th July to collect him. She is now saying that she is keeping our money and will refund it if she can get him sold to someone else soon, but if not she'll consider it part of her expenses for feeding him in the meantime!! What do we do?