Thank you all for the advice. :)
Well, she was a right case! I paid for the item, then left low stars and negative feedback, stating that she was refusing to post and relisting due to wanting more money. Then I reported her for seller non performance. Then I sat back and waited.
The next thing I know was that she'd left me positive feedback together with the claim that I was a "nightmare buyer". Cheeky cow! 
So, I politely pm-ed and said I'd already paid and asked for my refund. She replied with,
"Please give me your details for your bank account and I will send the money next week! I don't have paypal now. Do you want to wait 21 days for your money then I refund?"
Ummm... hang on... you had Paypal only a few hours earlier and you've relisted the item so must offer PP to prospective buyers. Nice try love but it's not happening!
So I responded with,
"I'm sorry, I don't give my bank account details out to strangers over the internet.
If you no longer have Paypal then I must presume that you're no longer able to buy and sell on Ebay. Ebay's rules insist that sellers MUST offer Paypal as a means of payment.
If you are unable to refund me by Paypal that's not a problem - I'll refer the matter back to Ebay and file an Item Not Received report at the same time, and let them resolve the issue."
Lo and behold she decided that she does still have Paypal after all. An hour or so later I got a pm to tell me that my Paypal account had been credited with a refund. Well, fancy that!
Meanwhile, Ebay were fantastic working behind the scenes. They assured me that Mrs Misery Pants was being sanctioned and removed the "nightmare buyer" comment from my 100% flawless feedback.
Mrs Misery Pants wasn't going quietly though. The note with my Paypal refund read, "I refunded ! Sorry because your are UNLUCKY!"
I don't think she likes me very much. 