Surveillance video shown in a Mississippi court Wednesday showed teenager Carly Gregg texting on a phone in the middle of her kitchen, in what seemed like a normal scene from modern American life. What wasn’t shown in those frames was that moments earlier, three gunshots were recorded by the video that prosecutors say took place when Gregg, then 14, shot her mother to death, according to the New York Post. Gregg, 15, is charged with killing her mom, Ashley Smylie, and shooting her stepfather, Heath Smylie, in March after they learned she smoked marijuana. The March video showed Gregg holding h…