2 female cats not getting along

Question
Hi my name is Adrian and I have a yr old American black short hair cat name Ayden  and recently I took in a new kitten name Aerial, I believe it's a tabby. Aerial doesn't pay Ayden much attention but Ayden acts real nervous, hissing and growling at her. I've kept them seperate unless I am alert enough to watch them both. Ayden isn't declawed but soon will be. Is there anything I can do to get the tension level down because I'd like to see these 2 roam around without supervision. I know it will take time. Please give me
guidance, opinions, and tips on what I can do to make the situation better.

Answer
You might want to try Feliway for calming your nervous cat: http://www.feliway.com/us
I haven't personally used it, but the feline-only vet I work for recommends it, and several of her clients have had success with it.
Make sure each cat has their own separate litter box as well. it's part of the "terriorial" thing between cats.
I have also personally dealt with this problem by associating their presence with good stuff: for example, we would feed our more agressive cat canned food (a great treat) in the kitchen across the room from our other female cat, gradually moving the plates closer together. The other cat now even steals food from her plate while she's eating without even getting her to growl.
More than likely, even if the two never are best of friends, they will eventually learn to have their own comfortable areas and live in at least semi-harmony.
Keep an eye out for fights and have a water bottle handy and squirt your hissing cat as soon as she starts an attack. I swear by water bottles as the most humane way of saying "stop that behavior". Good luck!