Item lost in the mail

[mustlovedogs2222]

Hello!  I have a confusing situation so I'm coming to the experts! :)....I sold a necklace to a buyer, and it promptly got lost in the mail.  We waited a while, and then I refunded her money.  Since then, the item has arrived and she wants to give my money back to me.  She would like me to send her an invoice, but I'm not sure how to do that....does anyone have any ideas?  Thank you for your help!!