If I remember correctly, Mr. King based Carrie on two girls he knew in high school. (Maybe they should break their silence as well.)
I think many writers get their ideas from observing or hearing a truth, and then expounding on it in their stories.
I guess because he's actually said Dennis Rader's name in connection with A Good Marriage, the daughter felt she had to say something.
Exploiting the victims? I don't believe so. It's been a while since I read the story, but I don't think the victims were focused on much at all. Like Mr. King stated in the article, it's about the wife, not the victims. He's not using anyone selfishly or unethically which is basically what exploiting means.
She may be horrified and embarrassed that she didn't realize he father was a monster (as we all would be), so she thinks focusing on that aspect is offensive. To me, it's just a look into how the innocent are affected by the guilty. I do feel very sorry for her to have to live with the knowledge of her father's crimes.