bushy tail - aggression or fear?

My 1 year old cat has recently started fighting with my older cat. They got along well until last week. The older cat will just be sitting there, and young kitty gets a bushy tail and charges. I've read a lot stating that the bushy tail signifies fear, but she always seems to be the aggressor. Both are fixed. This is definitely not play behavior. I've been trying to give them their space, separating at night, when I'm not home or when they fight. Any insight? This has been going on for almost a week, and I'm about ready to get rid of the younger cat (even though I love her dearly).

and welcome to TCS. How long have you had them? Especially your younger kitten? Is she spayed? How did you introduce them? Could there be stray cats lurking outside your home?
There are so many factors that could be relative to this behavior. Most importantly still a young kitty. If you already feel like giving up, then that is probably best while the kitten is still young, easier to find a new home.
In the future you should think twice about bringing in a new life to your home, if you can't handle it, don't do it......

It could be your young one wants to be the boss. Usually they settle it among themselves. It may take more than a week though.