@Kristen410 Extortion is against Airbnb policy. This guest is trying to extort you for a good review, and you don't even have any assurance that she won't leave a bad review anyway.
What is unfortunate is that she made this extortion threat over the phone. You should insist that guests communicate with you on Airbnb messaging, so there is clear documentation.
I would now Airbnb message her something like "Hi XX, so following up on your phone call earlier, you are saying that you will leave a bad review if we don't refund you? "
You want to try to get her to acknowledge the extortion in writing, so Airbnb can see it.