My first child was born with severe learning disabilities. There was no nursery that would, or even could, deal with her complex needs. I couldn't go back to work. There is no nursery provision for working parents of disabled children. When your child is born with a very obvious disability it's all on you. There is no outside agency to step in and help. There is no magic NHS thing, or community thing, or social service thing that steps in and tells you what to do. You have to go figure and sort it out for yourself. There is no nursery you can farm them out to.
My mother would not be left alone with my dd1 even for me to go to the toilet for a wizz. I had to take her with me. My daughter could take a fit at any time and DM didn't feel equal to dealing with it. And I don't blame her. It scared the shite out of me as well.
In an ideal world, grandparents dote on their grandchildren, and so will I if and when I get some. I can't wait to dote on them and play with them and love them and do all I can to make them feel secure and loved. (I have younger NT children - managed to drag them up somehow alongside my eldest SN child, and they are at the stage of starting families) But would I want to commit myself to regular childcare for my grandchildren? That would be a resounding no.
Would I take responsibility for a one year old grandchild in an emergency situation? Of course. In a heartbeat.
But in a situation where there is at least a month's warning then I'd expect there to be alternative options. If I was unwell and had a dodgy back, and the child wasn't walking I would demur.
There is also the question unwritten, between the lines.
What is the nature of the child? This is known to the OP and her DM.
My own dd2 was a lovely good natured child who walked at 10 months and didn't need to be picked up, was a delight to spend time with, had excellent language and communication and was easy going and amazingly, had really good concept of basic reasoning.
Which is just as well because dd1 was a fucking nightmare.
My mother, when she was alive, would tolerate a half hour while I had a shower entertaining dd2. But I had to take dd1 with me.
So I suppose what I'm saying is that if OPs Mum doesn't feel equal to looking after her grandchild for a whole day, why does everyone jump on her for it? There might be a really very good reason that she doesn't want to. It doesn't mean that she doesn't love her grandchild.
Perhaps the child is particularly wearing or difficult or badly behaved or given to tantrums. Or like, in my case, I took my god daughter to the cinema, thinking I'd give her mother a few hours peace, and the child not only ran me ragged, but started to do little gymnastic moves over the balcony. I was in lumps of sweat and rags after.
Other people's kids are such a huge responsibility.
It's not that you don't want to look after them per se, but sometimes the responsibility for their safety and welfare is overwhelming and a huge burden.
When we read a post, we only hear one side of the story. I can understand the responses from women who have really close knit families who would just step in without question. I really envy that.
And let me make it plain, for all the people who claim to have spent their childhood at their grandparents house being entertained and looked after while their parents lived irresponsibly and virtually child free lives - most of us really didn't.
People my age, which is 62, were lucky to have any living grandparents at all. All four of my grandparents were dead before I was born. And that goes for all my peers So to say it was the norm for grandparents to supply childcare in days gone by is not true in the vast majority of situations, Wealthy people it's different. They seem to live longer. Who knows why?
So it's a very 'now' thing that grandparents are expected to spend their retirement providing childcare for their grandchildren after spending years of childcare for their own children and then mistakenly thought that they could spend the final ten or fifteen years of their lives without responsibility? Because they've given their children the deposit for a house ( they did OP, didn't they?)
And every minute of their consciousness worrying how you are getting on.
So yes. YABU. They are your children. You have absolutely no grounds to expect your mother to look after them for a whole day on her own. She still loves them to little meatballs. She loves them.
However, she doesn't want the responsibility for a whole day. If you are fully mature you will understand that.