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Cat aggression is the one of the number one behavior problems cat owners deal with. There are many reasons why a cat would behave this way. There is redirected aggression, non-recognition aggression, petting aggression, territorial aggression, and so on.
To help calm her aggression get some feliway from Pet Smart. This is a pheromone that induces happy calm feelings in cats. Is great for aggression, anxiety, urine sprayers. You can get it at petsmart in a form called comfort zone.
If the feliway doesn't do the trick, try some Rescue Remedy.
To help her get along better with the 10 month old cat try a recognition technique where you pet one with a blanket or cloth and then pet the other and vice versa. This will accustom them to each others' scent again. Remind them they are buddies. Do this technique while you are alone with each cat. Not while both cats are present in the same room.
If she has issues with you or other persons petting her, this is called petting aggression. This is a dominance thing. She is showing you she is the dominant (alpha) cat in the house. I am not saying she looks at you as a cat, but she feels that she is the dominant species in the home.
You can retrain her to teach her that you are dominant figure in the house.
When she jumps up for attention, put her down immediately. If you have to stand up then stand up and move so she can't have access to your lap. Do this for a couple of weeks. Then when you allow her in your lap, don't let her decide when pet time is over. You cut her off first. Just pet her for a second put her down and then give her a kitty treat. The treat will teach her to associate the petting with the nice reward. Don't give her kitty treats any other time.
You gradually increase the petting time, but always be the one that decides when enough is enough, not her.
If the claws are an issue during her attacks, you can try getting some soft paws put on her. These are plastic covering that go over the claws. You can get these as well at petsmart.