I completely agree with everything you said. However, I also think she was doing it partly to help him. Another reason for her actions might have been for her to gain agency in the world where she had none, but that is just speculation. I look at the disbelief she expressed when she realized that he actually might have died, and I also look at the expression in her eyes. In many people who are on trial for committing crimes, I feel that I can glimpse moments of triumph in their eyes when the deceptive mask falls away. I don't see that in her. I only see grief and remorse and resignation.
I have a tendency to assign blame to parents of people who commit crimes when under about age 22. (I think the parents should be punished right alongside their kids. Public whippings, perhaps. It is quick and leaves a painful impression and saves on jail costs.) After age 22 or 24, the influence of the parents should be diminished to the point where a person becomes themselves. This belief probably stems from my own experiences, in which my mother tried to erase me as a person and my father stood by and did nothing to defend me while being perfectly aware of what she was doing. Getting away from them made a huge difference for the better in my life. For the record, I'm sure I was mentally unbalanced at 18. I just hid it very, very well.
In the case of the woman in question, I get the impression that she was not approved of by her parents (I know, I know, I can't know if that's really true or not), which is something that is often experienced by out-of-quadra children, and if she is an ESI, she additionally probably wanted to help and was also driven to make her plans come true. @
FDG has said that once an ESI decides on a plan, it is very hard for them to see that plan not completed. She just didn't foresee (low Ni) the consequences of her plan going into the worst-case scenario.
I'm not saying that she didn't exhibit extremely bad judgement. She did. But I'm also pretty sure that five years away from her parents will help her tremendously, and that she's in no danger of repeating what she did.