If your dog won't go up to someone, that is not protectivness; but I would suspect it is fear or at least maybe a little shyness esp. at her puppy age. For true defense the dog would be at the end of the leash pulling to get at the threat, not barking to try to scare away the scarey thing.
Wouldn't want to really count on a dog with behavior like that (at least from the little I can assume from your brief post and not seeing the dog in actual action. It is hard to interpret, of course.
BTW, just between us, a dog that istruly to be a protector is exactly the kind of dog who will go up to people calmly and socially. the toughest dog i ever met- once the top scoring dog in protection at the German national Seiger show (want a more protective dog than that?) once was walked around a dog show by my wife (didn'tknow the dogs history) perfectly calmly and met a number of other folks! THAT is what I would want a true protective dog to be like and with an ideal temperament!