What to call great grandma??

Ha
So we are having a name issue in my family. My grandma will be getting her first great grand child (by me 😉) in February. She just wants to keep being called grandma. But my SOs parents will be the only grandparents for our child (it we will probably be the only ones giving them grandchildren) So naturally they will be grandma and grandpa. 
What should my grandma (babies great grandma) be called. Noni is out, that's what she called her great grandma and it makes her sad.... Please help!!!!! 😊