Ebay will not do anything until she provides tracking for the returned item and when she does return it, feel free to pop up to your local police station and have a copper witness you opening the box (I did this once before), if its empty report the crime as fraud, get your crime ref number and a print out and send it to paypal they will deal with her then.
As for requesting refund before return
do one love!!!!!
Just keep your messages nice and state quite clearly that once returned refund will be issued, until then there is nothing you can/will do about it.
If there are no messages written on the dispute for 10-15 days it automatically gets closed by Ebay and your money returned to you.
I had an Aussie guy claim for a "Damaged item" wanting a partial refund (He wanted £100 back on a £200 item), asked for pictures for proof of damage, he sent me pictures for a different item, quick call to paypal and case closed.
Also if she threatens you with negative feedback unless you comply then thats for Ebay to remove after she leaves it (just did one this morning for my fathers account, guy left neg feedback and the guy was demanding money back for delivered item (Tracking proved delivery) and says he will agree to change feedback when he gets his refund
, thanks Mr German con-man you just threatened feedback extortion, Ebay can remove that for me now
(Which they did in 2 minutes).
Quick follow up email to buyer stating feedback removed, ebay and paypal informed, your blocked form buying and Ebay are aware of your ISP, any further attempts to do this will result in removal from Ebay.
Stick with what people are telling you and remind her that Marks and Spencer don't give a refund until the item has been returned