My friends GSD is three yrs and has a problem when people leave the house, it doesnt matter who just anybody walking out the door, i have never seen any of this but my friend says that she gets all stressed and my friend has to get hold of the dog and try to shut her up she said that the dog winds her self up so much. Why could this be i could understand if it was the dogs owners going but just anybody seems a bit strange this is not my breed so i do not know why.  Any advice thankfully taken.

GSD's are a herding breed, and as such can be very reactive to movement - it could be that she perceives the movement to be unauthorised by her owner, and requires attention.  At the moment it sounds as if the owner is actually rewarding the dog by paying it attention.  To manage the problem could the owner get up before the guest leaves and shut the dog away?