I do not think you are completely at fault, especially with Marc Jacobs as some admittedly do look very similar. I still have no idea why your buyer didn't pay closer attention to the pictures though. Anyhow, having said that you don't want to lose the bag and your money, so take the bag back. Ask that she put 'returned merchandise' on the customs slip or you may end up having to pay duty on your own bag!
Also I do not believe you are under any obligation to return the shipping costs (?).
Hope it all works out!
Also I do not believe you are under any obligation to return the shipping costs (?).
Hope it all works out!