Question on two cats who don't get along

First off I would just like to say hello and introduce myself to the forum, as I am new. I am fairly impressed with the information available on this site. However, I have been unsuccessful in finding answers to a problem similar to this, using the search feature. My name is Ryan and I have two female cats, Siciliy (3 years) and Stella (11 months). Both of them are spayed and only Sicily is declawed (front). Prior to acquiring Stella I had Sicily and a older male cat. These two got along great, but Sicily had been around him ever since she was a kitten. When I got Stella, I introduced the cats slowly over a weeks time. The male cat and stella got along well. However, Sicily has not cared for Stella too much and still doesn't almost a year later. My girlfriend (whom the male cat belonged to) no longer lives with me. Stella shows no visible signs of dislike for Sicily or any aggression other than failed attempts at playing. Sicily is not aggressive towards Stella, but if they come in close proximity of one another Sicily will hiss at her and run away. They have no problem being in the same room as one another and will sometimes sleep in the same area, just distanced. I am hoping that someone may give me some advice as to how to help Sicily feel less threatened by Stella, and hopefully get them to get along well enough so they will play with each other. They both are extremely playful cats and Stella tries often to play w/ Sicily to no avail. Any ideas?

If it is a year now, they may never get to the point of playing with each other. You could try a complete new introduction process, but I would think it is too late. I got Ellie as a companion for Dushka but although they tolerate each other they have never been really friends. Sometimes they hiss at each other and there is the occasional swipe, though they will all sleep on my bed. On the other hand, as soon as Persil joined the household, Ellie and she have been inseparable. Someone else may have better advice.

It's been a year, so really separating them and reintroducing them to each other would be a waste of time and only necessary if they were ending up in the vet hospital repeatedly with fight wounds. For now, you can try buying a Feliway Comfort Zone Room Diffuser and plugging that in, and looking into the Bach Flower Remedies. Look into Beech or Holly to help you out-

Thanks for the advice. I will look into the mentioned ideas. I really believe it is some sort of hierarchal issue. Sicily is very much a one person cat. She is skiddish around anyone but me, and really is only affectionate with me. She tolerates petting from other people who are familiar to her but you can tell she isn't very comfortable. Granted over the year they have been together, she has gotten better towards my younger cat, but whenit comes to eating Stella will have no problems eating around Sicily and always ends up eating first because Sicily won't eat if Stella is near the bowl. If they ever fight it is mainly just hissing and crying coming from Sicily with Stella just antagonizing her, but this is a rare occurance. Is it possible that my older cat feels intimidated by the younger one and that she feels her once alpha position is threatened and that is why only Sicily seems to have the issue with there being this other female cat around?