This is not from My 600-lb Life.  This is Mayra Rosales, from the TLC documentary Half-Ton Killer? She confessed to murdering her 2 year old nephew by rolling over into him.  However, it turns out she was just covering for her sister, the boy's mother, who had hit him in the head with a hairbrush. She later went on to lose 800 pounds.  Still fat, though.