why oh why oh why oh my!

Ebay is just great - but sometimes some of the people make me want to SCREAM!
Sold a pair of great big PRADA BLACK PATENT LEATHER sneakers - size US 10 womens. Gal receives them and emails to tell me that the size must be wrong because they don't fit her. Well, they are marked size 10 and belonged to a woman who wears a size 10. Perhaps they just don't fit this person - that doesn't mean they are not a 10. She wants to say that the size is wrong because that would mean that the item is not as described and she would get back her shipping.
In any event, when she emailed me to tell me that they didn't fit I told her that she should send them back to me and when they are received, refund will be issued. Seems fair, yes? So she emails me to tell me that she feels she must open a case with eBay. Now please tell me, why would she want to do that? Does she have any reason to open a case? What more could I possibly do to have pleased her? There is no reason to open a case. You open a case when the seller tells you that you can't return the sneakers - or you open a case when you return an item and a refund is not issued.
I deal with 1000s of people. 95% of the time people are more than satisfied with the item that they have purchased. When they are not, I ask them to just return the item - they do, I issue credit - case closed.
It really aggravates me when someone comes along who obviously does not understand the way this should work.
UGH!