You're getting a lot of hateful responses - but, as a grandmother myself, I don't blame you at all. I'm sure you have good reasons for not wanting to do childcare. And, after all, you have made it very clear to your daughter that you will not be doing childcare and it was, I assume, her decision to have children, not yours.
I did do childcare - I did an afternoon a week, one night a month, a couple of days every half term (once they were at school), but this was arranged right from the start. I offered what I was prepared to do and nothing else was expected. I was, however, prepared to do the occasional day/night in an emergency IF I could. I was working and already changed my hours to manage the one afternoon a week and used my own annual leave to cover the 2 days every half term. That arrangement worked for us. She also knew that I would drop everything to help if she had to go into hospital or something similar. Now my grandchildren are in senior school and I am retired due to ill health I don't do as much, but there is an open invitation for the children to stay overnight if they want to, and if I am able to.
Only you will know your own situation, and that of your daughter, but given that you have already let her know that you won't be doing childcare, for whatever reason, on the face of it you would not be unreasonable to say no. If it was me, and I was able to do it, I think I would say yes but make it very clear that you will NOT be doing it in the future. Perhaps a child minder, rather than nursery, would be a better fit for her circumstances.