Certainly she bears responsibility for her mistakes. But he was the only one who could fix his problems, and he didn't. And he helped bring two children into this world, and put himself above them. They will forever be damaged and angry with him etc. I think most of her letter is in defense of them. They are totally blameless in all this, and probably get the most "punishment" out of anyone.
Those who are the least to blame, shouldn't suffer the punishment for actions of those who are more to blame I guess is my thought, and I think that's where she's coming from. She's worried about the kids, not herself.