Big on going Probs with PILS, they have one of our clubcards - they spend alot at tesco and with thier points and ours we were able to take DD to some fab places last year there is no way we could afford to without them - for instance - lego land, warwick castle etc, etc...
They seem to use the card depending on if we are in or out of favour, It has been explained to them in detail how much you get in value for points etc...and how it goes on days out for DD.
AIBU for thinking MIL not using her card when she is upset with us is petty beyond belief, and only affects the DD she is supposed to love, and its a way of doing something great at no cost to them and also hardly any effort save scanning the card at checkout! BTW i dont think they would benefit from the points themselves at all - as quite well off.