If it were my house, I'd separate Allie to her own "safe room" keep her there for at least a week. During this period, take old towels and rub one on each cat to collect her scent. Then rub the scent on the other cat so it will become a familiar and trusted scent, and leave the towel in the room with the cat.
After a week, try a slow reintroduction, carefully supervised. The minute Allie displays aggression toward Emma, gently but firmly remove her and give her some "time out" in her own room. When she is able to co-exist with Emma for a few minutes, pet them both, saying, "gooood kitty." The idea is to use negative reinforcement for negative behavior, and positive feedback for good behavior. Sit on a sofa with one cat on each side of you, so that they can associate petting and love with proximity to each other. Next, you can carry it a step further, by feeding them in the same area. Make sure the declawed aggressor stays with her own food dish, by using loving correction when she strays.
Sometimes all efforts fail and a declawed cat may simply be happier in a single-cat household, where she can get undivided attention from her human caregivers. You might very well ultimately have to find another home for Allie. If that happens, don't think of it as "failure" on your part, but that you cared enough to want happiness for all the cats involved.