Sounds like she didn't want to pay return postage, and if she has left you glowing feedback she must have decided just to keep the item anyway.  I would just reply to the message from eBay and say no the buyer has not returned the item, but has left positive feedback so no refund is required.  They should then close it in your favour.  Whether or not they will remove the defect you got when the buyer opened the case is another story, but if they don't you may just have to wear it rather than rock the boat.