Where is the motherly instinct?

I can’t explain my disgust with these next two monsters. It’s like way above my logical reasoning. The first one killed her son and slit the throat of the other but he lived. This less than a year she had an “accident” and drove into the river with them. Crazy, just fuckin crazy. Why didn’t she die and the boys live? Makes you wonder sometimes…And all she gets is life in jail? Come the fuck on, seriously. Let me slit her throat with a plastic knife. I don’t care how long it takes, let me do it till the bitch’s throat is open. When the boy that survived talked to the police, he tells them about how his mother blindfolded and duct taped his mouth. Then he could hear his brother screamin as his mom killed him.