Dawn,
Congratulations on your grandchild! We never referred to my maternal grandparents as either "Grandpa," or "Grandma," and many, many of my friends had unique names for their grandparents, like "Papap" or "Baba," and the list goes on virtually indefinitely. You can be whatever you want, and it sounds like you're still close to your daughter, so she's obviously aware of and sensitive to your situation. I imagine that you two will come up with something that works for you both.
Erin