I love
Georgina, and think it's a good way of achieving something like
Jean as a nn without actually using
Jean! Which is seriously dated. I've never encountered or read about a South African
Georgia, so whatever it is here, it isn't common at all.
I don't like
Georgie.
Jean or
Gina would be fine.
Georgina all the way!
Georgia is not just one place name but two, and I don't go for place names on people.
Georgiana is far too ornate, 18th-century people going all Latinate; and then there's the strange belief that it sounds or could sound like George+aina.