Oh, OP.
Firstly, congratulations on the birth of your darling baby, and fingers crossed for a swift resolution of the complications.
I am surprised that your Mum (any Mum) wouldn't be so overwhelmed with joy at the birth, while being consumed with concern for you and your recovery that she would have head space for making critical comments.
Has she often been like this during your life? Is she often critical and thinks that most things should be about her and her opinion?
Is she possibly so worried about you that she is deflecting into fussing about the name?
I am assuming / trusting that you have not named your Dd Fanny or Candida or something. There will always be differing opinions about names and not everyone can expect to like every baby name in their family. This one is yours and your partner's choice, she had her chance when she named you.
Do you love your name? If not especially say 'well, I don't love the name that you gave me, but I lived with it happily - my turn now to name my own child. We love it, time to focus on how gorgeous your grandchild is'.
It is also OK to be assertive and direct with your Mum (sounds like it would be a good tactic - start now, she will have many other opinions about your parenting choices!). If she says anything else say 'yes, we had that conversation Mum and there is nothing more to be said. And in truth I was upset that you chose that moment to criticise so I don't particularly want to go over it again'. And don't. Change the subject.
Good luck, enjoy your baby and look forward to retuning home.