Josephine or a name with the initials F. E. Frances?
I am guessing that Euphemia is too out there for you? That is where the nickname Effie comes from. There is also Iphigenia.
Maybe Barbara could have the nn Buffy?
There is a Native singer from Canada named Buffy Sainte-Marie and her birth name was Beverly.
It's pretty out there but I think Buffalo nn Buffy is adorable!!