Rich Lowry or ABC doesn't have to confirm she wrote the letter because she herself said she wrote a letter to ABC.  She never said the attributed comments about Israel however.  Let me ask a simple question: what is the source of the letter with the added Israeli comments?  The best I can find is a random Usenet post.  If I wanted to smear her, I could take the transcript from one of her speeches, change a few words around and post it.  Not that I disagree with the made-up statement by her, but the point is she never made it, we have her denying it, and the source of the rumour is unknown, the best source is some anonymous person in Thailand.