I don't know. How can you be mentally ill and not of sound mind when you methodically murder your children one by one and lay them out on a bed. Seems to me she was doing what she planned to do. Also the other one who let her little boys drown. You have to know what you are going to do. I am not in a contest here as to mentally ill or sound mind. Those horrid deaths of those innocent children at the hands of their MOTHERS come to my mind first and foremost. It's hideous yes and they should remain behind bars.
FACT: The one they loved and trusted took their lives.
That's just it --- she was too methodical --- too cunning and planning. She waited until she had a few minutes alone with the kids --- knowing full well her mother-in-law would be arriving soon so she had to get it done quickly. She waited until the short time she had alone with those poor boys. And to outsiders and family members she would pretend to love those kids.