Thank you TCL. I know she is entitled to a refund, what I am wondering is - do I instigate it or does she? Does it make any difference?
Ultimately she will get a refund, but the advice I've been given by the Royal Mail is to wait 'a further few days' to see if it turns up.
This feels unreasonable to me, but I wonder if it will show up as I had a similar case a couple of weeks ago, a buyer reported non-arrival after more than 2 weeks, then it turned up!