Oh, I don't know…..it seems to me that the older girl should be allowed to stay in her home. It is harder for older dogs to adjust, and the younger girl is still very young...she would be easier to place, and easier to adapt. But it would probably need to be a home with no other female dogs, and maybe no other dogs at all. She might be okay with another dog added in as a pup, later...but she apparently needs to be the top status bitch in the house.
I know it is tempting to "blame" the older dog (believe me, I KNOW)...but in reality the older bitch is probably just defending her place in the pack..not actually aggressing at the younger one randomly. The younger bitch is most likely the one creating the problem.
If you are in contact with the breeder of the younger bitch, she should be happy to take her back if things aren't working out
It is a hard decison to make. I wish I had a way to make everything work the way we want it to...I really do