It seems a shame that she couldn't get her daughter to pick them up from you, but perhaps she doesn't drive.
I personally would just send a polite message asking if she has a date when she will be visiting her daughter and be able to pick them up as things get a bit hectic in December and you are hoping that the day she chooses doesn't clash with your family commitments.
If she hadn't paid I would have cancelled the sale as buyer not paid.
If there is no reply with a date within a few days then I would cancel the sale as buyer unresposive and no pick up forthcoming. Then of course you will need to refund the buyer and re-list.
A set of eight dinner plates would sell fast this time of year, so this is a great opportunity to get them gone. However limiting yourself to collection only is making the availability very narrow. Dinner plates are heavy and need careful packing, I would split into two by four plates but put them in the same box. I can see you have experience posting breakables.
Hope this resolves either way for you.
