Our CHOW-mix has attacked our female GSD 4 times. Each fight gets worse. What can we do?

Our 3 yr old lab/chow (spayed) drew blood for the 4th time in two years on our 5 yr old GS today. Unfortunately, this time the GS has a serious wound and is staying at the vet for treatment. This was the situation this time: We live on a farm, and we had a new sheep (we have one other sheep, which the dogs "raised") brought in to the corral that is next to their run. The sheep was sniffing the lab/chow through the fence and Kota, the GS came over to get a sniff, and all hell broke loose. At first I was able to shout at Chemukh, "OFF"-she paused for a brief time, then went in harder until Kota retreated.

We recognize that the dogs have a packing-order, but we are not recognizing who is who in this small pack. Chemukh came first, then the GS, who by the way, at 105 pounds is exactly twice the other dog's weight. How does an owner tell who is the Alpha dog? Another variable is that that the smaller (meaner) dog has developed displaysia and is cranky. My husband wants to ship Chemukh off because we have a two year old child... he fears that she could get into the middle of one of these fights and get hurt. I am willing to work a little harder if there is something that we are not doing right. Do you have any suggestions? I greatly appreciate your very valuable site.

One more question, not training related, pertains to our GS. She is a beautiful large female that we rescued. We have no idea where she came from, only that she was probably abused (hand shy, afraid of anything resembling a stick, would run from the site of a rifle, etc.) She is a stunning dog though and we are approached frequently by people asking if we raise Shepherds. My question is about her coloring. She resembles your dog Gideon, only where he is light brown, she is white. Is there a name for that type of marking? Is it undesirable? Is it from a particular line? I have only seen one picture of a GS with the same color. Any info would be appreciated.