Mail Lost in Transit

Recently received a message from one buyer of my scrapbook stash, she has claimed that items have not been received and asked if I've posted out the items, however, this is not possible as I have posted the items on the very next day after I replied her. Of course, I have no doubts in her words, as I have heard of increasing cases of mail lost in transit among online sellers. It is with deepest regret that I do not have stock of all items she bought, so I can only replace her of what is still available despite that I should not be held liable for items lost in normal mail. And in addition , I've included some freebies, and hopefully, this will cheer her up... :)