Ewww! Please report!
Ugh! From the pictures you've shown, the bag looks fine but a picture of the creed is necessary to be sure.
Please direct the buyer here because she needs to understand a few important points.
1. The time to have asked questions should have been before bidding and buying
2. If she didn't have time to authenticate beforehand, she could have come here before paying to ask about the item
3. Coach is the last place to go for authentication, especially when that request is showing an ebay listing!!
It's no secret that Coach hates ebay, doesn't want to see their bags being sold on ebay (or any other website besides their own partners) and they're known to LIE to customers like your buyer when they know an item was purchased online.
Your buyer should come and express her concerns and if it turns out that Coach lied to her, she owes you an apology (pending a pic of the creed) and should end the dispute.
(ANd this isn't even taking into account that she opened a dispute without having even received the bag!)
ETA: Here's the listing:
http://www.ebay.com/itm/100-AUTH-CO...594?pt=US_CSA_WH_Handbags&hash=item2a155f6082