Hello @Valerie225,
No you haven't done anything wrong. Unfortunately guests are often under the mistaken impression that the host gets the money immediately when the guest pays.
All you can do is to point out to the guest thay you don't have their money, Airbnb does, and that you don't get paid until after checkin.
Airbnb will automatically refund the guest according to the terms of your strict policy. She will not get the Airbnb fees back and will get at most 50% of the room charge back.
The article below describes the refund time process.
When will I get my refund?
Steve.
If she's looking for a full refund of the room charge it's up to you whether you wish to do that. It will be at your own expense. You can use the "Send or receive money" link in their reservation to do this.