DID SHE POST A SERIAL NUMBER ON THE MACHINE? Write it down.
I would probably want the machine - since it's such a great deal. Seller's loss as far as I'm concerned.
I'd have to ask her WHY she's relisting the machine she ALREADY SOLD TO YOU? See if she'll admit it went for less money than she wanted.
I would report the situation to ebay right away and keep them up to date. Tell her you've reported her. Leave negative feedback.