A very honest post. Overit....
Been there, done it and like you , I am also tired. My daughter's children are 17 and 15 and I have been helping out from the day they were born, mostly with my time, but not so much financially. I have helped here and there, but don't do so now because I am retired and there's not much to go around.
My main grumble is that my daughter takes me for granted. I haven't heard from her this whole weekend, but I'm sure when the holidays are over, I 'll be 'contacted'.
I'm afraid to use the word 'most' grandmothers, because I was told off on another post, for generalising, so I won't. But most of us are being taken for granted, because most of us absolutely adore our grandchildren.
Do what you have to do. You seem to be a very honest, straight forward lady. Talk to your daughter. I'm sure she'll understand. When my son asked me to help out with his little one, I explained that I am now too old and couldn't do it, on a regular basis. He understood. His parents in law do most of the nursery runs etc. Good luck !!