My Tabitha (17 years old) hissed at Sasha (now 2 years old) when they were first introduced when Sasha was a kitten. Now, they "tolerate" one another! Sasha still chases Tabitha through the house, and often "lies in wait" for Tabitha to appear! Poor Tabby, all she usually wants is to spend some time on Meowmie's lap! So she just jumps on my lap and gets comfortable and looks at Sasha like "hehehehe!"

Give them some time, I am sure they will learn to love one another!