Franca can also be spelled Franka.
I find just plain France kind of a bold interesting move. Might be safer as a middle name. Pretty, but there's the whole I see London, I see France, thing...
Freya (????) Maybe with a certain middle with sounds from the -nk part of Frankie, like, Freya Nicole.
Fannia (a stretch, as its a variant of Fanny, another nickname for Frances, but, could work). Maybe give it an R middle name with a K sound too for good measure. Fannia Raquel?
I also find Fiona nn Frankie a bit much, and I'm flexible on these things. At the same time, do what you want : D. People have nn's that have nothing to do with the name sometimes. I'm Jessica/Jess and went by Nina as a pet name for several years (although it never left the house/expanded beyond my parents).
I love all the suggestions,Thank you! And please keep em comin! I actually knew a girl named France (Fr-AH-nce) Claire, she was from...France haha! That's a very interesting option I hadn't thought of. I also like Frances, Freya, Francisca and Francetta. Could/Do you pronounce Francetta (Fran-CHE-ta)?