... and if I may suggest that you put a follow-up against the feedback you left for her (assuminig you did so) that says something like...

"<UserID>: Refund given due to item reported lost in post <date>"

The userID is important as part of the comment so we can see who it is and add her to our special lists if we wish to.

That way all other sellers can see when they look at her feedback that this has happened and if all sellers do this then the track history becomes very clear and a permanent part of her FB, and may stop her from doing it in future.

We normally send out replacements rather than refund so our comment says "replacement sent".