Hi Kristen!

I strongly suggest separating the 2 for approx 2 weeks. That way Luna can slowly get used to Lily's smell. You may even have to give her more than 2 weeks. Rub towels on each of them and put the towels under their food bowls. That way they can smell the other cat while they're eating.

Luna's reaction is very normal. I am fairly confident that with seperating them and introducing them slowly, Luna will come around. She is still young and will probably learn to like having a ktity around

Good luck!