Narnie is really cute! I imagine it might get mistaken as
Marnie, which seems to be getting a little bit of attention right now due to the Girls character and
Lily Allen's daughter.
It's hard to think of a full name that works well. Maybe something with Nar rather than Narn, like Leonarda or
Narcissa? (I don't like
Narcissa, but it seems to work.) I've seen Nairn or Nairne used as a name before.