When I brought Missy home Sassy was pissed, even at me! She wanted nothing to do with Missy. Of course I had a way to keep them separated and Missy was a kitten at the time. They get along pretty well now but Sassy is well, let's put it this way, my friends from work call her Satan!
Can you get a hold of a large crate? I know crating a cat sounds funny but some people do it for short periods of time in this kind of situation. Maybe it would give you a chance to see if they can at least tolerate each other without anyone getting hurt.
Who knows, maybe Layla will surprise you! I wish you the best of luck!