Naraku's screams became different, terror changing the pitch, and it gave her a moment of clarity where she realized what was happening.
She had fallen into her power when she should have pulled it. Her own terror rose, and her eyes turned desperate as she latched on to the first person she saw in a plea for help.
Whether Sesshomaru took pity on her or recognized the signs of a burn out or something of a mixture of the two, she didn't know. She only knew she was thankful when she saw the subtle nod, and the step he took toward her.