I'll give you this, Trident, you can see what so many others easily overlook or simply avoid acknowledging: At one time or another, many, many, many parents have been on that line between motherhood and murder, be it due to mental illness, stress, exhaustion, or any one of a million different reasons.
I know we don't agree on this woman's potential motivations, but on the point above, we do agree. To be perfectly honest, there are times that my children have been left for a few minutes at a time to cry it out, simply because I knew myself well enough to know that if I didn't walk away, I was going to be in an orange jumpsuit on the evening news. Personally, I think that there are a great many children that end up dead (both newborns and older kids) because parents today aren't allowed to say that they are at the end of their ropes. To say that we are capable of harming our children, whether we ever have or not, is to admit that we aren't perfect, and in today's world, that just isn't acceptable. I don't know when parenting became synonymous with perfection, but somewhere along the line, it did.
Nothing can excuse what this woman did, but I for one do want to know why she did it, because none of the "usual" reasons seem to fit in this case. Either it was fear that drove her to it, long term and well hidden mental illness or she really is evil. At this point, we don't know, and you're right, we might never know for sure.