Ring eBay and ask for removal; if no satisfaction is gained then ask for the link to the Defamation Claim Form.  Complete it, get it signed by a JP (your local chemist) and then fax a copy of your PayPal account showing when she paid, together with a copy showing when the item was purchased plus the Defamation Claim to eBay.  If the feedback is untrue, it should disappear despite the fact you have left a follow up comment.:-)