You have to show your cat how to use appropriate items for scratching. There are scratching mats available or an old piece of carpet will work. Use more than one scratching post in areas near the couch. Cover the places where your cat scratches the couch with double-sided sticky tape, sandpaper or plastic. Spray problem areas with citrus or menthol sprays that won't harm your cat - there are a number of commercial sprays for cats that may work. Rub the places where your cat is allowed to scratch with catnip (the scratching posts) to get her attention.
