What was there to LIE about?
She drowned FIVE kids, one by one. She PLANNED it over time.
No, she's not insane. She was sane enough to PLAN this and CARRY it out and when done murdering them she CALLED THE POLICE. This is not an "insane" person. She earned capital punishment.
"What was there to LIE about?"
A prosecution expert claimed she was sane and merely imitating a law and order episode, which, in truth, had not aired at the time of the killings.
(The L&O episode was based on the killings, not the other way around, I think.)
You are absolutely correct. The legal definition of "insane" is not knowing the difference between right and wrong. Since she called the police, she knew that she had done something wrong. It seems pretty clear cut.