Indeed, I have a daughter with that name:)
Well, there really is no rule as to how to *correctly* pronounce names.
Nephele in the US would be pronounced NEH eh lee, in Greece it would be nef EL lee and, presumably, in
France nef el
LEE.
As for
Circe (KIPKH in Greek), the original pronunciation would be KEER kee which, understandably, could be awkward to the unaccustomed ear :)