I don't understand how the smell alone doesn't alert everyone within a block of her house
Well these babies even at full term, if killed right after birth, lacked the intestinal flora that cause most of the smell as the body decompose. Also because babies have a much larger surface area to volume ratio, they would dehydrate much faster especially in a low humid environment... speeding up the mummification process.
As for the crime... clearly the woman is psychotic-insane. Although her crimes were horrendous, I don't think that kills her right away would accomplish anything.
I think she need intensive treatment to restore her sanity... then show her the graphic pictures of what she did.... finally abandon her in Death Valley without water/food/shelter so she will slowly die like her babies!!