Dog Barking, Barking

As a new pet in the house, my mond was totally oky with it and spoiling the dog with treats. A month after his graduation party, i'm outside with my dog, walking her behind the garage to go to the bathroom,. The neighbors out in his yard think he's doing yard work, and he comes over, andMy dog just starts growling and barking and growling. And this is a growl we only heard a handful of times throughout her 14 year life. This time it's even more vicious than the last. I'm apologizing to the neighbor, saying, i'm sorry. I don't know why she does this. As the dog continued to bark