What's funny about this entire thread is:
#1, this entire hassle is about $15 ($20 total). Refund the money and move on. Tell her to keep, or eat, or do anything she wants with the shoes. These people are not worth your time, especially for $15.
#2, you seem to think eBay gives a damn about you, the seller. You seem to think that reporting a user to ebay will do something. Sorry to be so cyincal, but ha, ha.
#3, you seem to think eBay will support you in "following the rules". The "rules" only work for eBay, not for you. See #2.
#4, I saw no "feedback extortion". She wants to work something out before leaving a negative or a positive. If you you think YOU are in the right, and don't care about the potential negative, then tell her "all sales final" and move on. You can't please everyone. If you think reporting this user to eBay for "feedback extortion" will do anything, see #2.
Sorry to be so overly negative. You have to try to work your problems out without eBay. I've had over 8 years of eBay and their BS. If it wasn't for the fact I still make some pocket money, I'd have nothing to do with this two faced greedy monster.