Since she filed an item not received (INR) claim that makes things a little more complicated.
You already uploaded tracking to the INR so that's good. In a few days you will be able to click a button and ask eBay to step in. The INR will be found in your favor because tracking confirms a delivery attempt.
After that's settled you can try to send a partial refund, though I'm not 100% sure the system will let you. But you should try it as the next step. You would find the transaction on your orders page then in the actions column select "send refund" - on the next page enter the amount you're refunding. Choose the reason "other" and fill out a brief comment. You'll need to wait until after the INR is closed to try this.
If the system kicks out an error saying something about not being able to refund since a case was opened on the transaction (the INR) then you'll need to rely on the buyer's honesty and cooperation for the next step. You can tell the buyer to open a return request and use the reason "changed mind" - then when the request comes through you would approve it and send a refund without a shipping label since the package was already returned. As long as the buyer uses a remorse reason like "changed mind" then you can withhold original shipping.
Come back and let us know if you have questions along the way. I know there's a lot of "if" scenarios and a lot of info to unpack here.
