The character level for this fight: 71 (Knight). The weapon for this fight: Sword.
She is the 12th boss in the Dark Souls 3. She has 2 large long swords. You should attack her from behind and move in circles around her. The main advantage is that she is rather slow. You will be able to attack her and have time to protect yourself. Use your shield. You need to block all her attacks. After this attack her with two fast attacks and allow to restore your stamina. You have to block, then to attack her and do the same again and again.
Run away and hide when she starts to swing with her swords. Her grapple does the considerable damage that is why you have to avoid it.