It is not practical to allow your cat access to one chair and forbid access to another.
She will not understand the difference between the two chairs and you will end up with a nervous and unhappy cat.
However, if you do not want her to scratch your furniture, there are several methods of training.
If you are in the room, keep a water gun or spray bottle full of water at hand and squirt her the moment she starts to scratch.
If she likes the water (yes, some cats do) then throw a rolled up newspaper or a bunch of keys in the floor near her.
The loud sound of the magazine or keys landing, as well as the surprise, should stop her scratching.
Be sure your aim is good, and remember, the objective is to frighten her away, not to injure her.
These methods are good as long as you are awake and in the room.
For those other times, try confining her to a room or pen so she cannot scratch the furniture.
If this does not appeal to you, then tape orange peel to those areas where she likes to scratch.
Or cover her favorite scratching areas with clear heavy plastic, available at pet stores.
Another suggestion is to attach a small scratching post to either end of the couch or chair.
Do not try the trick of inflating rubber balloons and taping them to furniture to make certain areas off limits to her.
The balloons are dangerous and even fatal, when punctured and the remnants inhaled by her.
To discourage your cat from scratching the furniture, attach orange peel to it, she will hate the smell and quickly back away.
Although a cat flap is a good way to allow your cat access, it is also an invitation to neighboring cats.
To avoid this, you can buy an electronic or magnetized cat flap than can be activated only by a special collar worn by your cat.