The best method is to stick close to her and whittle down her health in between strikes. You gain more posture damage from countering than hitting her, but her health going down makes the posture damage last longer. As well, when she goes up on the line of thread, ensure you're dodging when she dive bombs you as this is a grab attack that will more than likely one shot you. And last tip, ensure you stay close to her. If she gains distance on you, she throws shurikens that are obnoxious to dodge, and during phase two they spawn in the center of the room as well to "home in" on you.
Here is a video, all credit goes to PS4Trophies channel (make sure to leave him a like if the video helped), that shows how another player did it. He makes note of using the shuriken to knock her off the thread. I found that this only works sometimes, but it may be a "chance" to knock down and may work for others more often then not. Anyways, good luck and enjoy!