I cried, "Oh, Lady Midnight, I fear that you grow old, the stars eat your body and the wind makes you cold." "If we cry now," she said, "it will just be ignored."
I don't know why it says Kate nods as if reluctanctly agreeing with Jack. It appears to me that it isn't clear as to what she thinks. Although, it does look like to me that she could be a litle baffled as to such a strong statement from Jack.
( "If Locke comes back he's going to kill him? " )
This is quite out of character as far as the person we know Jack to be, but we also know that in the future he starts plummeting down a very dark path. There's something that subtly takes him that way and so I'm sure we can expect more of that same in the future, I'm pretty certain.
At any rate, it looks to me as if she chose not to respond and direct the conversation in a totally dofferent direction, avoiding confronting it head on. And Kate is very good at avoiding facing stuff head on when she doesn't want to.