I do tire of the insanity plea. When terrorists have been beheading folks everyone says they are evil. Could it just be that she's evil?
It sounds more callous and cold-blooded to me. Are insane people always so calm? Maybe she didn't want the child anymore so she butchered her.
I remember seeing a case of a woman who was in severe PPD and her husband, instead of staying home to help her when she was in obvious distress, went to play golf all day on a Saturday. He returned and wanted to know where the baby was -- she didn't even REMEMBER the baby and it took forever to find out she taken the baby out, drowned and buried it and then gone home and to bed...
There's plenty of women and men who physically abuse their children or in some cases one of many children, and I have absolutely zero sympathy for them when they kill their children. PPD is not in the same category.