Old cat not accepting new cat

Hi everyone! I'm new to this site. I have an 8 month old kitten and have had her for about 6 months now. She is our only pet besides my two parakeets. She goes with me to my parents' house nearly every weekend, and she is around other cats and dogs there but is scared of them. I just recently decided to rescue another cat.
I got the new cat home and followed the advice most people give about separating the two for awhile and let them smell each other. Well, my 8 month old would growl a little but was never mean towards the smell. But once I introduced the two face to face, my original cat hisses at the new one sometimes and growls when the new cat gets too close when she's not expecting it. The new cat, however, wants to play. This makes it difficult, because the new cat will playfully pounce towards the old cat and the old cat gets scared and hisses and runs. I am afraid that this will be how they act with each other forever. Is there any way I can get my old cat to accept our new family member? I make a point to pay as much attention to her as I did before, maybe even more attention. Please, if there are any suggestions, help!

My cats do this when I bring a new one home but it never turned into anything. If they came into contact with each other and haven't tried to kill each other yet they probably won't. But you never know for sure. I would first of all, stop taking your 8 month old home to your family's house. Especially if she is scared of the dog and cats there. She will never get over this fear of you continue to tramatize her like this.

So stop that

Also when you are home, continue to have them together in the same room but put some vanilla on each of their heads, back of neck, base of tail first so they smell alike. Let them hiss and growl a bit but be sure it doesn't get out of hand. Have a blanket handy to throw over them if they start to fight. Good luck.

Skit did that to Jett and Jack too, but after a couple of weeks everything was fine. He would mainly hiss and growl but then he'd walk away. At night I would separate them just in case it got out of hand. But during the day when I was around I let them all hang out together until they got used to one another. Sometimes it takes a while and sometimes you don't have any problems. Patience is the key.

It looks MUCH worse than it is, My friends vet told her "Basically if there is no blood, everything is fine."

I've just gone through this with My 2. The Old kitty would be sitting at the door Hissing and growling and the new kitty would roll around and try to play with her. You just have to give them time. Make sure they both have safe places to go away from eachother for now too, and don't force them to socialize. It only took about a week and my two a romping around the house and fighting over my chair, I caught them licking eachother last night hehehe.

It really helps to establish a routine and remain relaxed about it. Routine makes them feel safer. Also, the feliway comfortzone plug in is amazing.