It's not a secret that Mrs. Bush is pro-choice and she hasn't been hesitant about saying it.
This is an author's account of a private dinner conversation. Four people were present. Since I am quite sure the author was not one of the four, he is getting his information either from one of the principals directly or is inferring things from gossip and others' conjecture.
I know for certain that the President and Mrs. Bush would never disclose a private conversation. I am also certain that Tony Blair would not.
Therefore, we are left with Cherie as the only person who could possibly have spoken to the author. Somehow, I don't think this is an accurate accounting of the conversation, myself.
It was until I read your post.
While I wonder if I should assume she's anti-gun and pro-illegal invader as well, we can be thankful at least she has enough sense not to broadcast it.