in Chapter 6, how did mrs. Whatsit battle the dark thing?

Meg learns that there is more to Mrs. Whatsit than meats the eye. She has powers of the metaphysical that she uses to fight the Dark Thing.The Happy Medium implores the children to look into her crystal ball again, and this time they again see the Dark Thing, but also a bright light that touched the darkness. When it touched the darkness, the light disappeared, and the Medium assures them that “it can be overcome.” When Charles Wallace asks what is happening, Mrs. Whatsit tells them that it was a star doing battle with the Dark Thing. The star won, but lost its life in the process. Mrs. Whatsit then informs them that she herself had once been a star and had done battle with the Dark Thing, which is why she has fallen into her current form.