My mum was the same, wanted me to go down to hers for christmas 11 days after DS was born. I said I just couldn't, that life was totally upside down. 3 times she called me to go down, and tried to guilt me into it.
She also didn't like the Grandmother/Nanny options. She was 60, and remarried the year I was PG. she even said she never wanted to be a GM.
I'd let yourself calm down about it and in the new year call her up and talk to her, or better yet go down and meet her somewhere.
Tell her straight. I did mine, albeit a good while later, once she had got used to the idea and was doting on DS.
I said to her that our GM had helped her when I was born, that she was the same age as mum and didn't come out with this I'm too young to be a GM bollocks.
I told her (gently) that tbh her attitude was really selfish. Did she expect me NEVER to have a family just because she didn't want the GM title?
I was 38, so not like I rushed into anything!
I told her that she had her time to be mummy, and now it was my turn. That now she could see how great it was to be a GM, that she ought to reflect on how sad it was for her to behave as she did, and how it will always make me sad to think of the early days. It could have been so much better.
So OK we have got there in the end, and in the scheme of things this is only a blip in life, so you will get over it, whatever happens.
Oh and if you are sitting waiting for a call, it could be that she is scared of waking the baby, so call her yourself! 