What does the tracking show?
It sounds as if the buyer didn't receive the item because she was not at home. Is that what happened?
The tracking information should show if the item is on its way back to you.
If you have tracking that shows attempted delivery, then the case opened by the buyer will eventually close in your favour. You would need to add the tracking to the case.
If the tracking does show attempted delivery, and that the item has been returned to you, you could wait to get the item back before you refund.
"There are two ways to be fooled. One is to believe what isn't true; the other is to refuse to believe what is true.”
Søren Kierkegaard, Danish philosopher (1813 - 1855)