If the buyer's deadline has expired, contact eBay/PayPal and try to get the case escalated and closed in your favour. Opened cases count in your defect rate:
- The defect rate is simply the percentage of a seller's successful transactions that have one or more of the following transaction-related defects, the top predictors that a buyer will leave eBay or buy less:
- Detailed seller rating of 1, 2 or 3 for item as described
- Detailed seller rating of 1 for shipping time
- Negative or neutral feedback
- Return initiated for a reason that indicates the item was not as described
- eBay Money Back Guarantee (previously known as eBay Buyer Protection) or PayPal Purchase Protection case opened for an item not received or an item not as described
- Seller-cancelled transactions
- Cases found in your favour don't count. Any case that escalates to eBay or PayPal for review and is found in your favour, or found to be no fault of the buyer or seller, won't count against your performance rating. It won't be counted as a defect and it won't count toward your percentage of cases closed without seller resolution.
http://pages.ebay.ca/sellerinformation/news/springupdate2014/sellerstandards.html
Then it's up to you to decide how to help this buyer.
"She never even let me know that she hadn't received the item prier to filing the dispute."
If the buyer bought the item while logged in on either eBay.com / eBay.co.uk (not sure if the German site has this too), sending a message may open a case against the seller.
It's possible that the buyer tried to contact you, but she accidentally opened a case instead. Here's a sample thread from the US board:
http://community.ebay.com/t5/Seller-Central/Opening-cases-instead-of-sending-a-message/td-p/19559517
