They understand their defenses have been taken away
Really? I've never had a declawed cat, but I do have a three-legged cat -- one of his front legs was amputated before I got him -- and he still tries to use his missing leg, though it's been years since he's had it. (Okay, so in a way, I suppose I do have a declawed cat, but depawed is more accurate....)

When he plays, he'll often try to bat at something with his missing paw; when he wants to cover something (he sometimes editorializes about his dinner), he stands on his three legs and tries to use the missing leg to cover whatever. If he wants to attack the little cat (or me), he rears up on his hind legs and lifts both shoulders and his one front leg; if he still had the other, it would also be up with claws bared. He doesn't seem to get that that leg just isn't there anymore. He always looks shocked or annoyed when he bats at something with his missing paw and nothing happens. He can't bat at stuff with the one front paw he does have, because he'd fall over if he did.

Now to the subject of the thread... apparently, cats don't like the feel of aluminum foil, so wrapping wherever she's scratching the chair with aluminum foil may work to keep her from scratching the chair. Worth a shot; cheap fix if it works.