My mom has my kids call her GI GI and my mother in law is omi
Tell her you came up with something else instead of nanny granny will work for you
Have your kids call her grandma and that's it if you wanna get under her skin lol.
My mom is nana and my moms is just grandma Marsha if your not comfortable with you baby calling her that then just flat out tell her no that'd to close to mum
My kids call my mom mama and that's only bc they started to and iam mommy and every other grandma they call them grandma and then there name there's nothing in books that say they have to have a nic name