Shelly, I had the same kind of thing happen when I had 2 female spayed German Shepherds. The older one (Kara) and younger one (Mia) were 3 years apart in age. I hadn't known about pack mentality...I have had 5 dogs at a time and never had one problem. I think the fact I used to take the 5 dogs out on a lead to potty may have been key with them. But with Kara and Mia I would let them both run out the back door into the 100'x100' fenced yard to potty.
One day when Kara was around 8 and Mia 5yrs. old they were in the back yard and Mia went after Kara and held her neck. Thankfully, I was able to separate them and didn't think it would happen again. A couple weeks later it happened again only this time in my kitchen! Neither was hurt from either incident. From that second time on they were separated by rotating them...one would be in a crate and the other in the kitchen and vise versa every several hours. It was a pain to have to do that but it guaranteed no fighting. This went on for 5 years until Kara passed away at 13.
When I got Bentley I was more versed in the pack hierarchy. He was 4 months old when I got him spring of 2009 and then got Baxter, my Boxer that September. I kept Bentley the alpha by petting him first, taking him out first, eating first (both had to sit to get their food) and treats first. I don't want to jinx this by mentioning they are best brothers. I don't let them stay in the house loose when I am gone for any amount of time.
Maybe you can restore Moka or Mylee (whoever you believe was alpha or was there first) by feeding one of them first, etc. I know how upsetting it is to go through this and I hope you will get it all straightened out. By the way, I still have Moka's valentine paper heart on my fridge from years ago!!
