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

Cadsuane is an Aes Sedai that shows up mysteriously. The other Aes Sedai seem to defer to her. Cadsuane does not revel what her intentions are but does say that she will not hurt Rand more than she has too. She goes out of her way to help Rand, but Min is still concerned over Cadsuane's motives.