I agree ^^ It sucks that she is trying to back out last minute, but if she paid through paypal, she can file a SNAD on you and she'll probably end up winning it. I know how irritating it is for you, but it will help you in the long run, if the amount of the item is more than $250, you must get a signature for the delivery of the item to be protected under paypal seller protection. That being said, she can refuse the package, and file an item not received, and you would be out of ebay fees plus shipping. Ebay + Paypal is a big pain in the butt for sellers, good for buyers though.
Also, there is no way to dispute a negative feedback because of the circumstances in a transaction, feedback is an opinion, and all opinions are valid on the feedback page. Unless, they have invalid contact info or been a ebay user for less than 30 days and become NARUed, sorry the neg stays. A neg will always hurt the seller more than a buyer.
There is a common misconception of "final sales" or "as is sales" on ebay. It's true if you only take a payment forms of money order or check, but when taking paypal: NO SALES ARE EVER FINAL. Sorry I know that's not what many want to believe, but it's true...