firstly, do NOT refund anything until you have the set back and in the condition it was sent, and make sure it is exactly what you sent her.

secondly, your auction stated

Returns:7 day money back, buyer pays return postage

so there it is,  however, I would state that I was not willing to accept a return for 'change of mind' ...

if they want a full refund, they should go thru the PayPal dispute, and let PayPal make it clear to them that they will have to return, by a trackable means (ie.Registered Post etc), at their own cost,

if it's not exactly as it was sent, come back here for more info.