The woman has been known, for quite some time, to be suffering from post-partum depression. The officer first on the scene noted that she(the mother) was clearly shocked, saddened, and confused by what she had done in fact, it was her who called the police.
Though it's too late for this woman, this event could have been prevented. Not saying someone else is to blame, just saying that one day, with increased knowledge on PPD, events such as this won't/shouldn't happen.