I honestly don't know, but you really need to call the credit card company ASAP and ask them what to do, and get the vet to fax over his letter to them ASAP. Like now.
The sooner you start this process, the better. If she lives and they tell you that you need to give her back in order to get your money back, you can always change your mind and just keep her and loose the money.
If she dies, you are on your way to getting your money back. If you wait, you might be too late to recover and money and then you will have no dog and no money.
I'm so sorry to sound harsh, but she is very tiny, very young and very sick, so it's a possibility.