It is very moving to read, Toe -- I agree. In fact, I think that many people would have welcomed it before now, and I kind of think she has more to say. There's a big gap right at the end, understandably, because this appears to be her first attempt to speak about something that was a major trauma in her life and was then complicated by someone else's celebrity and a different narrative of the same trauma.
Although I can understand how she felt when she first read Capote (and then has had to cope with more Capote since), I don't believe that testifying -- which is what good writing always is, fiction or non-fiction -- is ever a zero-sum game. Maybe she will always be angry at Capote for telling the story he did, and she obviously needs to get that out. Fair enough. And maybe, because she was so close, she will never get past that anger. Also understandable enough. But the truth is that she has her own story and she can write it, so she should.
I don't believe that Capote did anything wrong in producing that great book, although of course he could never do justice to the Clutters because he never knew them. She did and she can, so she should. In a way, the one has nothing to do with the other, although if she could write out as well the emotional struggle she's gone through living with Capote's narrative as a second trauma, that would be a great story too.
Capote knew the killers and he was fascinated by them, one of them especially. He wasn't alone, and that's not strange either. Those killings were so brutal, so apparently inexplicable, that people couldn't help trying to understand. How could that happen to such people, and why? Who would do that? Obvious questions, and those were the questions Capote pursued.
I don't think it's entirely true to say that Capote made the Clutters cardboard figures, either. It's been a long time since I read the book, but Capote narrated the murders in excruciating detail -- derived from exhaustive interviewing locally and interviews with the killers -- and some of that detail is still in my mind. I remember especially how father and son died in the basement, and I remember the tenderness with which both Capote and her killer (obviously) spoke of Nancy -- just before her killer blew her away. I'm sure that was beyond unbearable for Diana to read, but I will never forget Nancy.