EBay would NOT have given them the opportunity to add a postage cost to a free post listing, because it is against their policy. My guess is she has seen the postage box in the invoice, so taken it upon herself to add the cost (probably thinking eBay gave them the opportunity to do so).
I would remind her that she has now violated several of eBay's policies and that could lead to her account being closed down. I would also contact eBay again (by phone) and explain that she offered free postage, she accepted the best offer, now she is trying to charge a postage cost after sale. Not only that, she has now relisted the item while the transaction is still open.
I would imagine there is nothing in her ad to say that the final price didn't include postage? Even if there was, she still advertised free postage. If she remains stubborn, and I don't say this lightly, hit her with a red dot. Most new sellers are happy to be educated by more experienced members, but she is digging her heels in and not budging.
What does she think will happen if someone (stupidly) buys it for that price, then you decide to pay? Who does she send the dress to?
I would take a guess and say she wasn't born here by her reference to "dear friend". That is a common Chinese greeting when you ask a seller a question.
