Everyone's financial situation is different. Why can't some people grasp that?
It may well be that some people have always been treated by their parents, until they are well into middle age, because their parents have plenty of cash....well lucky them (or perhaps slightly selfish them if they have never ever, in all that time managed to treat their parents, even if their parents are absolutely loaded) but surely everyone can see that not all parents have lots of cash, and as with everything, you can only have what you can afford.
Here Op was very honest about the money situation and DD was given a choice, and she chose to go for the meal and to pay. There was absolutely nothing wrong in that and nothing for DD to be ashamed of or to have to apologise for. There is nothing to say all children regardless of their parents financial means are entitled to any form of gift or treats at any age, and certainly not as adults. Lots of families are very hard up and don't get lots of the things other families might have or consider the absolute norm or even entitlement. So lots of families can't pay for school trips or for holidays or for social outings or for new clothes or all kinds of things....its the reality. If, as those kids get a bit older and financially solvent, they choose to pay for something for their parents, then that is totally their choice and nothing to be ashamed of.
Op, be proud of your DD. She has the maturity to see that a meal out with Mum would be a nice evening, that couldn't happen unless she paid and she willingly paid. She preferred to do that than for you both tho miss out on the nice experience. Good for her, just receive it graciously and if your friend comments again, tell her how proud you are of your DD and that families help each other out....you support your DD and she supports you...its all part of being a family and everyone just does what is needed...there really isn't anything to say that parents must always pay for everything at any point, and actually it's selfish if adult children to constantly let their parents pay,me dan if they are wealthy...whatever happened to treating others and finding the pleasure at can give. Perhaps some of those rich parents would thoroughly enjoy it or benefit from learning to receive graciously as well as to give.