Have you opened a dispute on eBay with this, or has she done this already? In this process you both get the chance to have your say, and eBay will make the decision. I must admit that if I don't agree with someone complaining that "item is not as described" I will always offer a refund but only once the buyer has returned the item in the condition I mailed it to them. She can't return the item so she can't have a refund - she has bought it then disposed of it. I just have a feeling sometimes when people make an unreasonable fuss like this, that she is wearing the skirt but just wants it for nothing. Have you checked her history on eBay (by clicking on her feedback record)? This might not be the first time. The key thing here is to respond to the dispute, if you don't then eBay have to make a decision in so many days - and say that you would have been quite willing to refund on receipt of the returned item. eBay are reasonable, I have had no problem with them when disputes have been raised but your buyer sounds like a stinker, and trying it on.
BTW cassa, I have had no problems with PayPal, unless a dispute is found against you by eBay then the only person who can initiate a refund from your PayPal account is you.