Sophie is NOT just a nickname. It's a full French name. I heard of
Sophie long before I heard of
Sophia. To me if your going to call her
Sophia, name her
Sophia; if you're going to call her
Sophie, name her
Sophie. They're two distinct names.
Trying to say that
Sophie isn't a full name, but a nickname for
Sophia, is exactly like saying
Claire isn't a full name, but only a nickname for
Clara.
Claire and
Sophie are the French versions, though they are OCCASIONALLY used as nicknames for
Clara and
Sophia.
Just something I needed to get off my chest :).
Hope you understand.