Update From Cindy Sheehan on her diary at Kos (via AfterDowningStreet.org):
Another "big deal" today was the lie that I had said that Casey died for Israel. I never said that, I never wrote that. I had supposedly said it in a letter that I wrote to Ted Koppel's producer in March. I wrote the letter because I was upset at the way Ted treated me when I appeared at a Nightline Town Hall meeting in January right after the inauguration. I felt that Ted had totally disrespected me. I wrote the letter to Ted Bettag and cc'd a copy to the person who gave me Ted's address. I believe he (the person who gave me the address) changed the email and sent it out to capitalize on my new found notoriety by promoting his own agenda. Enough about that. (Emphasis added.)
This is not a clear explanation. The letter existed in the form that includes the "My son joined the Army to protect America, not Israel" statement on March 20, as it was posted on bullyard—before Cindy Sheehan's "new found notoriety."