Carly Madison Gregg was convicted after jurors were shown chilling surveillance video of the teen
Gregg sobbed in court as she learned her fate.
"Carly Gregg is evil and that's not easy to say, but the truth of the matter is that sometimes evil comes in young packages," said Rankin County District Attorney Bubba Bramlett.
The jury saw five days of disturbing evidence, including surveillance video. In the video, you can first see Gregg with a gun behind her back as she paces around the home. Then, you hear gunshots.
Gregg then returns to the kitchen, and is seen texting and playing with her dogs.
Prosecutors say she shot her mother, Ashley Smylie, in the face.
Smylie was a 40-year-old high school math teacher.
Then when her stepfather, Heath Smylie, came home, Gregg struck him with a bullet.
His frantic call to 911 was also played for jurors.
"Gun went off in my face before the door was open," Heath Smylie said on the stand.
The stepfather then wrestled the gun away, making that frantic call to 911.
"She killed her mom," he could be heard saying to dispatchers.
Prosecutors say the violence unfolded just hours after a friend told Gregg's mom about the teen's marijuana use.
Gregg's attorneys argued she was having a mental health crisis.
"She doesn't know what was going on at that time. We're asking you to find her not guilty by reason of insanity," Gregg's defense attorney Kevin Camp pleaded with jurors before their decision.
"I put three in my mom and I got three -- I got three more waiting for my stepdad," state prosecutor Kathryn Newman reenacted. "You think that sound like an insane person? No."
It took just two hours of deliberations for the jury to find Gregg guilty on all charges. The defense says they plan to appeal.