Dog fight problems:( pls help?

I have two female dogs, both are about 5 years old. About a week ago our staffordshire terrier grabbed our boxer by the top of the neck and refused to let go. This happened as me and a few friends were just coming home. luckily the boxer was unharmed. the dogs were introduced again and we had no problems for a couple of days. then when my mom came home from work, it happened again. We went to the vet and were told that the staffordshire terrier was getting over stimulated when someone comes home. Is it likely that the staffordshire terrier could get over stimulated and turn on a human like it did the dog??? it breaks my heart to ask this because i love this dog, we never thought that she would turn on her best friend:( pls help