Andrea was barely functional and in a religious delusion fostered by Randy and his crazy belief system. I doubt seriously she was reading about a 40 year old case in Hawaii that was basically unknown.
Mothers thru recorded time have often drowned their children - just as women thru time more often use poison instead of guns or weapons to kill. She didn't need to find the idea, it was already there in her sick mind. Andrea is severely mentally ill - not just postpartum psychosis but bordering on schizophrenia.
She wasn't right before she killed her children and sadly the mental health professionals and the lack of proper insurance for mental illness failed her - just as it has failed countless others. Munchausen's By Proxy, chronic infanticide, post partum psychosis, acute bi-polar disorder, schizophrenia are ALL disorders than without treatment can lead to innocent children and infants murdered by their mentally ill mother. Left untreated and with disinterested or enabling spouses (like Randy) they can kill. Andrea should have been hospitalized and prevented from having more children long before she killed. Mental health hospitals and proper facilities for those who are a danger to themselves or others should be a priority - sadly we have high priced rehabs on every corner, but no facilities for people who are poor, underinsured or just too sick to be un-supervised.