The Guardian calls it “an act of love:”:
I wasn’t there when she told our children what she was going to do, and gradually I began to realise that they understood her intentions rather differently than I did; that our daughter, particularly, was more aligned with Elizabeth’s views than I was. So I wrote her a long letter, arguing that I was in favour, but only when it became necessary; only when Elizabeth’s quality of life had declined so much it had become intolerable. It seemed to me that she was jumping the gun, talking about doing it fairly quickly, perhaps not even reaching her birthday, which I thought was crazy.
– hat tip to Art Caplan