GSD to protective over our family

Question
My 7 month old GSD and we have only had her for a month. She is great with my two kids, my husband and myself, but when a stranger comes over even my mother and father, she barks very aggressively and even nipped at my dads arm twice.  She does NOT have any aggressive tendencies at all besides that.  She is only to protective or territorial.  Please help!

Answer
Getting her spayed should help if not already.  Move quickly if not.  She could be coming into season any time with all the hassles of the discharge, attempts to get loose, chances of accidental breeding, etc.  

The important thing is to be giving her the leadership she needs.  Dogs see all the people and dogs in the household as a pack with each having their own rank in the pack and a top dog.  Life is much easier if the 2 legged pack members outrank the 4 legged ones.  You can learn to play the role of top dog by reading some books or going to a good obedience class. A good obedience class or book is about you being top dog, not about rewarding standard commands with a treat. Start at http://www.dogsbestfriend.com/  For more on being top dog, see http://www.dogbreedinfo.com./topdogrules.htm  If you are top dog, then it is your responsibility to control the strangers that come around.  She can just follow your lead with them.