What an interesting subject.
My boys are raised without a daddy. So one day at school they ask my oldest " whats your fathers name?". He responds "I don't have a father but I have three moms, Mommy, Mom and Grandma".
Me being Mommy.
It had never occurred to me to have them named. He just listen to me call my mom Mom and hearing me called Grandma to his great grandma.
Let us know when your granddaughter arrives.