Armorica
this is what the coast of Northern France used to be called around 1000 AD. I think it's a beautiful name for a girl. It's ancient, unheard of, easy to pronounce, and doesn't look or sound like it's been made up just to be different. (just in case: ar-MOR-ica) I don't know what kind of nickname you can get out of this.
Armorica is the Latin name for the northeastern part of Gaul given by the Romans, including present-day Brittany and part of Normandy. It comes from the Gaulish are-mori meaning "near the sea." Because of the geography, this may be considered an alternative name to the popular Brittany!