I’m a bit against the tide on this one. I think Dontcallmelove might have got inside your Mum’s head, ie maybe she’s got to the age where she just had enough of shopping? Presumably she’s elderly, maybe she just doesn’t want the fuss any more.
Is she still buying for her 2 great-grandchildren (soon to be three)? If she is surely that’s enough? Even if your Mum has enough money she may not have the enthusiasm.
Because you ‘enjoy treating people’ and ‘buying presents’, I think you’re being a bit judgemental, albeit on behalf of your daughter. For older people it can be a chore and a worry. And does your daughter really mind that much anyway? You’re making your decisions about buying presents, as is your sister, your daughter is making hers, allow your Mum to make the same decision.