With the upcoming changes guinsoo’s will give 24% bonus AD, and with an infernal drake or whatever she will have enough. Early game she can just toss on a long sword or a cull or something to complete the 100 AD requirement. Or even better, a 500 gold pot that she can pop before a close range fight to upgrade her Q:
There is no good reason to buy a whole item.
Her AP W is her Raison raison d'être. It procs her passive three times, giving it MUCH more scaling than it officially has, and much more overall damage. With that being on a ~4 second cooldown at max rank with max cdr, she is better off using the rest of her kit as a finisher when going AP.
There’s just no reason to justify buying death’s dance in particular. She doesn’t deal much physical damage at all. If you must build an attack damage item, get a triforce or a guardian angel. Both will benefit her significantly.