Are both your dogs neutered? Maybe there is a hormonal issue causing dominance? I have owned both a male Australian shepherd & a female. We now have found the neutered female showing dominance toward our Australian Cattle Dog. She is two years old & we have had her since she was 8 weeks old. She will wait for him to come in through the door from outside & growl & snarl. I have to contain her by her collar. The male Australian Shepherd I had years ago never growled or snarled at anyone. I had an Australian Cattle Dog bitch that would sit on cats & take the other dogs toys & place them under her so they could not play. I have found the female dogs over the years to be dominant even after they were neutered. Maybe it has to do with the breeding & bloodlines?