nike, my post was directed towards the OP: "My question is: is it possible that I have over socialized her, so that she will not become a good guard dog? From some signs I would say no, for example we have changed our bell 3 times (!) and from the first day she knew that someone is coming (good sign) and was waiting in the door to greed him and/or play with him (not a good sign)."
hulk, chances are that if a person was truly motivated to intrude upon your home and/or family and going about it in a semi-intelligent way, they would scope out the place first, notice the dog, poison the dog before the break in, or prepare themselves to kill it upon entry. Some intruders may not care about the barking or risk of being attacked, opting to skip directly to killing the dog upon entry. Drugged people, for example, can be incredibly strong and insane. I have seven (alert) dogs, including three big dogs who look quite menacing, but I have no delusions about their ability to protect me from a truly motivated intruder. About the only thing I could hope for them to do is be alive and barking to alert my neighbors, and for my neighbors to hear them and not think they're just having a "dog party."