Sorry this happened, but it really does pay to understand what is going on when selling online.

As an inexperienced seller, putting up high priced items for sale is always risky. 

What you now need to do is get her to pay for the item. She doesn't get to keep it and get a refund.

You should write her a firm, polite and short message to say that should she not pay for the item, you will be forced to take legal action. Firstly, you can send her an invoice through Paypal and give her 3 days to pay it. Explain that she needs to settle the issue, otherwise it will be handled over to a debt collection agency.

Another forum user had a great bit of text to use to facilitate this with the buyer. @countessalmirena - could you rustle up your past explanation of how the seller should go about this?