I am with the OP and understand exactly what she means. I fthe family go somewhere, say the zoo, their DD, will leave them to pay for the tickets for the family, and the ice creams, and the little things to take home. If you are on a pension, even comfortable ones, these 'little' extras' can, week by week add up until they account for well over £100 a month, or more.
I suspect it happens because, as children, we are used to our parents picking up the bill, and then when we are first working and money is tight, parents still pick up the bill, until it is an unthought about habit that when out as a family, the parents/granfparents pay.
My personal belief is that these matters should be dealt with openly. If you are uncomfortable about this, find a reason to trigger the discussion. next time a joint outing is planned, where you will just be expected to pay the incidentals, just suggest that the outing be postponed a week or two, because you really cannot afford it this month and then explain why, quickly, briefly and in a casual manner, not accusatory.
The rising cost of petrol and geberal inflation gives a perfect reason, why your expenditure has to be curtailed.
I am sure the problem is just that it has not occurred to your DD just how much you are spending and that it is an issue.