I only see Charlie as a nickname for Charles - only for a boy. At least it wasn't Charlize. Anyway, I guess it could be a nickname for Charlotte, but I don't think nicknames should be planned, but left up to the child.
I really like Charlie for a girl. maybe you could have two names as her first name(Anne-Marie, Mary-Kate) and just call her Charlie for short? like Charlie-Jane, Charlie-Ann, or Charlie-May.