If Grandma had contracted norovirus or fallen and broken her leg, what alternative childcare arrangements would be made?
She didn't say she wouldn't look after the child, she said she would look after the dog and the child if child was taken to her house. I don't think this is letting down anyone, it is in fact helping out both of her daughters simultaneously so that no-one was let down.
Remember the granddaughter is the new kid on the block, the dog has been around for longer so why should the dog be treated as less important than the child. If the dog was not an animal but a human, what would the poster think.
Reading between the lines there appears to be problems between the two sisters and their Mum is trying to keep the peace. Remember Grandma has done her childrearing and was probably looking forward to living her own life while she is young and fit enough to do so. I imagine she enjoys looking after her grandchild, but doesn't need all the drama that comes with it.
The poster sounds like a drama queen threatening to uninvite her mother from the wedding and not letting her look after the grandchild - sounds like blackmail to me.
I'm intrigued to know what all the wedding stuff is that is all over her house. How much stuff do you actually need for a wedding. I can feel another non-drama coming on. I'm surprised she isn't going for the quadruple whammy and moving house in addition to having a baby, getting married and starting a new job.
How long the new job lasts is debatable as she gave up her previous job when they denied her request for flexible working hours. Is that even an option where she worked or was she expecting them to accommodate her as well.
I think she needs to look at herself as it might be her who is the problem.