I currently have a year old bitch and a 7 year old male - we have never had a fight yet - there has been the old scuffle but the bitch is still quite submisive so nothing has ever come of it. I really don't think you'll have a problem, maybe when you girl has matured she will be the more dominant dog - but that will not neccessarily mean fighting - they decide their own pecking order and many dogs live in complete harmony.