Consider yourself lucky that she is acting like a guard dog, and you didn't even have to train her to be one. As long as this is the reason she barks, then you have a great alarm system, and it just may pay off in the future. You just never know who might be at your door - it might not always be of a friendly nature. My 2 little ones used to be excellent guard dogs, and nobody came on the property without them telling me about it. Unfortunately one passed away a few months ago, and the remaining one doesn't hear as well as she used to, so I get no warnings anymore. I really do miss that!