Strongly recommend using short sword for the fight, don’t use big sword.
When you are close to the golden Undock, you may want to parry her slash attack. So it is worth it to learn the timing of her attack. If you don’t want to parry, roll left/right when she raise her hand to attack you. Later on when you fight the black Undok, notice how she can summon two types of lighting. Roll back when she touches her sword and electricity starts to flash around her body. If she summon circle of electricity that surround her, continue to stay away. If she summons lighting that randomly shoot down on the floor, I recommend you take the risk of running toward her and go just crazy. You may get struck by a lightning but it is worth it.
The video is not mine and credit goes to the creator of the video. The player attempted to win the fight without taking any damage so he run around throwing spears. He dragged the fight longer than it should be. You can be more aggressive and use health items later. When both enemies (golden and black) appear, keep focusing on the one with lowest health. Leaving two enemies on the battlefield is a real pain, so finish one off quickly will help a lot.