I was friends with a
Frances who was always called
Frances. So I don't think
Fran or
Frannie is inevitable. But it all depends upon how a
Frances would feel as an adult. You could bring up a daughter always calling her
Frances, but if people started calling her
Fran or
Frannie as an adult and she either didn't mind or actively liked being called
Fran or
Frannie, then
Fran or
Frannie it would be. My rule is to not use a name if you dislike any of its nicknames.