My cat destroys the sofa no matter how many scratching posts I put out.

Having four scratching posts and still losing the sofa is one of the most frustrating things cat owners describe to me, and it almost always comes down to the same thing: the posts are not matching what the sofa is offering. Your cat is not being difficult. She is telling you exactly what she needs, and right now the sofa is the only thing in the house that delivers it.

The corner of the couch is a very specific target. Corners offer resistance on two surfaces simultaneously, which is something most posts do not provide. The height matters too. If your posts are shorter than her full stretched length when she stands on her hind legs, they are not giving her the leverage she is looking for. And the material of the sofa, whether it is fabric with a weave she can catch her claws in, matters more than most people realize.

Before adding anything else, I would look carefully at what the sofa has that the posts do not: height, angle, texture, and location. Cats scratch where they feel confident and visible, often near where they sleep or near entry points. A tall, stable sisal post placed directly in front of the corner she uses most, not near it but in front of it so she has to choose, is usually the first real test. If you want to go through the specifics of her setup and what has already been tried, the Work With Me assessment is worth doing because scratching problems that persist after multiple attempts usually have a specific reason behind them.