Anyway, one of the coins in the little pot where she keeps these was this one:
It's a 1918 half-sovereign. I think she got it from her aunt — I remember telling her to keep hold of it, anyway, rather than throw it out. Why her aunt would have a 1918 half-sovereign is anyone's guess (she was only 12 in 1918).
I had a quick look on the Internet to find out how much it might be worth. As a lump of gold, it's around £60; as a collector's item, the answer seems to be somewhere between £125 and £500 depending on the condition of the coin and the ability of the coin dealer to lie to your face. As my mother could do with £125 (if only to pay the phone bill she's going to get following all the calls she made when my brother died), I've said I'll sell it for her.
I'll let you know how much I get for it...