Obviously there was at some point an understanding of what the dog would cost. You can establish payment with the money order through your receipt from the money order.
If you haven't paid the purchase price and you wish to keep the dog, she can sue you for the additional balance owed. If she lies about the price and sues for more, you and your friend can testify as to the actual understanding. As you apparently went to Texas to collect the dog, she should be able to sue you in Texas. You don't get "pain and suffering" damages in a breach of contract case.
If you didn't want to pay for the dog because it was sick, you should have returned the dog. It will be difficult to argue that the dog wasn't as represented, as you have nothing in writing, but you are free to argue that as a defense or counter-claim if she sues.
Did she attempt to deposit the check and have it bounce?
We have no way of knowing if she is actually trying to involve the police, and even less of a way of knowing whether a prosecutor will deem the case worthy of charges (or what charges would be authorized).

