Who is Cadsuane from A Crown of Swords and what is their importance?

Cadsuane is an Aes Sedai. She shows up mysteriously, and the other Aes Sedai seem to defer to her. Cadsuane doesn't reveal her intentions, but she does say that she will not hurt Rand more than needed. Although, she goes out of her way to help Rand, Min is still concerned over her motives.