Ok. You did exactly right. You calmed down. That is the best thing to do.
Now. You offered her a full refund after she returned the dress. That is exactly right. No return. No refund. Stick to your policies. Always try and kill them with kindness. If she opens a case against you etsy will side with you. If you are worried about negative feedback, just refund the money. But not until she returns the dress. Be firm ( but nice) on that front.
Best of luck to you....
hugs,
Angela