Jon's mom and dad have always been open to being called whatever Harper wanted to name them. We've been going with Grandma and Grandpa ("Granda") because she hadn't gotten attached to any other name. However, that has now changed. They will now be known as Nana and Papa.
We realized Harper had renamed Jane one morning when we asked if she was ready to go to Grandma and Grandpa's house. She looked at us and said clear as day "Nana". Well... oohhhkay then! "Papa" came about at their house one day when she just started saying it. Now she calls him that all the time so it's definitely stuck. Jane is thrilled as Jon's Grandmother (her mom) was "Nanny". Don's stepdad was always known as "PawPaw Cy" to Jon, so the names are close to home for the Hanes family. My Dad's mom was "Nana" for us kids, so it's a nice recollection for me as well since she holds a special place in our hearts.
Here is Harper reading with her Papa.