I suffer from the same problem OP, and my daughter is EXACTLY the same, and quite frankly all these people saying that you shouldn't tell her how you're feeling, are being far too generous minded about her attitude. I think we've all become afraid of saying or doing the 'wrong' thing with our grown up kids, because we worry that they have the power to stop us seeing our grandchildren, which is an awful way to live. I also think that if you can't tell your own family how you're feeling health wise, then who can you tell? When I was a child, we had a neighbour who every time anyone asked how she was, would go into long detailed explanations of what was wrong with her, when she last saw the doctor, etc., which caused most neighbours, including my parents to avoid her like the plague. We used to call her 'Mrs, Ooh me pains'! So when I first began to suffer health problems, I remembered this, and made sure that when asked how I am by an acquaintance, I just say, "I'm fine thanks", if it's a good friend, I say "I'm fine thanks" quite often followed by "well actually I'm feeling pretty rubbish, but that's life, how are you?" However, I think with family members, if they care enough to ask how you are, they should be genuinely interested to hear what is really going on. People say that our kids don't want to think about us being vulnerable, but an adult child should, in the natural way of things, be preparing for the day when we are no longer around to help out, etc. so why would we protect them from that? I honestly think that there is far too much pussy footing around with our kids these days, and it's leading them to think that they are the only one who matters.
Therefore OP, I do think that you need to sit down and talk to your DD about this. Tell her that you were hurt by her attitude when she asked how you were, and you told her truthfully. I would also perhaps make this the point where you tell her that you have now reached the stage where taking care of her kids is getting a bit too much for you, and while you genuinely love seeing them, you're no longer able to provide child care, if of course that's the way you feel. Don't use it as a way of punishing her, but if you truly are finding it too much, then don't force yourself to continue looking after her children, to the detriment of your own health.
I think it highly likely that on the day that your DD upset you, she wasn't thinking about anything else but the difficulties it will cause HER when you can no longer look after the children for her, and not, as all these kind hearted grans think, that she was actually worried about YOU!