Here's the link for feedback extortion. Frankly I'd hit eBay like white on rice reporting feedback extortion.
She can't detract her neutral. She can do a mutual withdrawal. The comment will be left and that's all.
If they find her to be guilty of feedback extortion her account will be NARU'd. If she's within her for 90 days..then her feedback will be withdrawn.
There are quite a few eBooks, articles and more explaining how to scam SELLERS on eBay, Yahoo, any site that has a feedback system in place. And what you described is one of the methods.
Queenie,I'm sorry this happened to you. Get with eBay immediately. Save all correspondence between you and she. Do you have a store, they have a phone number you can call? If you're a powerseller get on the horn and squawk at them that this is feedback extortion.