I don't think so now, HappyMum.
It's been a dreadful experience for you, but tbh, it doesn't sound like she's the sort to retract her feedback. That would be the only way of undoing this, I think.
I really wouldn't be put off buying from you because of one negative feedback. Some people are so twisted . Easier said than done, I know, but try to put this behind you. A bit more buying and selling and that negative feedback will be long forgotten