Hello - i'm new to this forum. And to me, it's really odd that i felt pulled to respond to THIS post, because I feel that my children don't appreciate me either.
However...when i was raising my son and daughter, things like your above mentioned situation would happen - i would call my mom at the last minute and let her know i wasn't going to go with the 'plan'. She never questioned it, or seemed hurt - it never occurred to me that it would hurt her! She just always went along with whatever whim i had at the moment.
BUT - i was always very nice, very respectful of my mom. I never insulted or tore her down her entire life, still haven't (i'm 52). I think if i had treated her badly, things would've gone differently.
I do think sometimes we have to demand that people act in a positive manner around us, or leave our home, our 'comfort area'. I love what Maya Angelou says about this, about not allowing negativity in our home.
I'm just now learning that people will treat me however i allow them to, even and especially my husband and children. I am in the process now of letting them know in many ways what i will and won't put up with anymore.
Sometimes it's just a matter of opening your mouth and stating your terms!!
As for those grandkids...your daughter needs YOU much more than you need her, as far as baby sitting needs, relying on you for all that mommy knowledge she hasn't acquired yet, emergencies, etc. While i don't yet have grandchildren, I am doing my best to gently guide my kids, on their own levels/needs, to treat me the way i want to be treated, because i've allowed myself to be a doormat all my life and i'm so sick of it.
good luck, and #1: be true to yourself!!! Everything else will fall in line.