What should I do about my cats suddenly hating each other?

I have two cats, one is about to be 7 and the other is 4. They're both female, and the older one is from a pet store, while the younger is from a breeder. When the younger one was first introduced, they had a bit of a stormy relationship, but it got better and they became friends... somewhat. But about two months ago, we moved, and suddenly the younger one started being hostile to the older one, who mostly growls and tries to hide. It's gotten so bad we need to keep them in separate rooms at all times, with two litter boxes, food, water, and whatnot. Is there any way we can go back to living the way we were? I really don't want to give up either of the cats.