Favorite Fabrics, maybe I too will open myself up for problems with my opinion but this situation is a perfect example for why many businesses "WILL NOT" ship overseas. Regardless for the reason for the buyer not replying to your emails it was her responsibility to answer.
You did everything within your control to try and help this customer.....they dropped the ball. Custom charges are the norm and while people get upset with them it's the law over there and they have to live with that when they purchase from the US. You have no control over that and should not be expected to cheat and write gift for the customer. That is just plain wrong. Also postage is not cheap sending there either unless it's a military P.O. box. People living overseas know this and outweigh the cost of the fabric or whatever else they may purchase to make the decision to buy or not to buy. It's not any business's fault the cost of items there and when they choose to buy from the US it is their choice and they know the cost of postage and customs for the items. If they don't then they need to be proactive and find out the facts.
You went way beyond the normal in trying to provide the best service you could for this customer. It is the buyer's responsibility whether it is a US or overseas customer to read the website and make themselves aware of your policies and shipping procedures. After reading many posts of unhappy people regarding their purchases it usually comes down to them not reading and informing themselves of the way the seller does business. That is their fault not yours.
So in my opinion you did the best you could and I wouldn't worry about their unhappiness as it is their fault not yours. You can't make everyone happy and for me it would not be a loss to lose this customer. You have many happy ones and will gain many more. Again, this is one of the main reasons people in the US will just not do business with overseas customers mainly because there are too many variables (things outside your control) that make things go wrong.
So please don't worry or think you could have done something better for this person. You did everything you possibly could and still got grief for all your efforts. It just isn't worth it to put yourself through that. People tend to believe it's always the sellers fault when in fact it is their fault for not being responsible purchasers.