If that was true then she wouldn't have been found not guilty by reason of insanity.I don't buy that analogy, she knew she had an on-going illness and knew how affected by it she had been in the past, but she didn't seek counselling, a heart attack is generally an unexpected occurrence.
I'd agree she was seriously mentally ill at the time of the killings but yet this illness did not preclude her from deceiving others as to her intent, everything she did she planned and subsequently formulated this plan so that no one would be in a position to stop her, so a lot of her actions were those of someone fully in command of their faculties. You may not agree but I think there was still an onus on her to seek help when she knew she was going downhill, so I do think she is culpable for the killing, maybe not at the moment she committed the act but certainly in the lead up to it. Should she be punished for this, I think she should.
Not everyone who commits a crime while mentally ill is not guilty by reason of insanity. The criteria is very narrow and it refers to situations where the person is not capable of understanding the nature and quality of the act they are committing.
You are seeking her to be punished as if she was sane when she committed the act, but she wasn't. It isn't a matter of whether or not I agree. This is a matter of fact, not opinion.
Also, she did seek help. Lots and lots of times. She wasn't a criminal mastermind who wanted to kill her children and then "get away with it". She was insane and in that insanity killed her children and then tried to kill herself.