Sandra Layne cried quietly when she heard the verdict, which was delivered during the first full day of jury deliberations. She was also found guilty of using a firearm during a felony and likely faces at least 14 years in prison for the death of her grandson, Jonathan Hoffman.
Defense attorney Jerome Sabbota said later that Layne was "devastated" by the verdict.
But some family members had harsh words. Hoffman's mother, Jennifer Hoffman, said her mother was a "monster" who deserved to go to prison.
"I'm glad she's put away and can't do harm to anyone else," Jennifer Hoffman said outside court. "He was a great kid and didn't deserve this."
His father, Michael Hoffman, said the verdict was a "final vindication for my son."
As Layne was handcuffed and being led out of court, some family members sitting with her 87-year-old husband, Fred, waved in a show of support. But she couldn't make eye contact because there was a deputy in between blocking the view.
Layne fired 10 shots at her 17-year-old grandson, striking him six times over a six-minute span during an argument last May in her home in West Bloomfield Township. She never disputed that she killed him, but she testified that she did so because he had hit her and she feared for her safety.
The evidence included a recording of Jonathan Hoffman's desperate call to 911 in which he pleads for help, even as more shots are fired.
"My grandma shot me. I'm going to die. Help. I got shot again," he told the dispatcher as he gasped for air.
Jurors declined to comment following the verdict, but they told attorneys during a private meeting that the 911 call was crucial to their decision. It revealed that Layne had left Hoffman bleeding but then returned with more gunfire.
"They said they played it over and over and over again" in the jury room, prosecutor Paul Walton said. "One of the big things they said is when you hear the shots on the (call) there's no struggle."
Sabbota said jurors found the "911 call was critical."
The Oakland County jury had a choice of first-degree murder or lesser charges, or it could have acquitted Layne based on her argument of self-defense.
In his closing argument, Walton told jurors that Layne never rushed out of the West Bloomfield Township home, despite claiming to be afraid of her grandson, and never called for an ambulance to help him after the shooting. She said she shot him after Hoffman struck her during a heated argument about money and a plan to flee Michigan because of a failed drug test.
"I wanted him to pay attention to me. He had to listen. It wasn't a conversation. It was arguing. Swearing," Layne said in tearful testimony last week, explaining why she pulled out a gun.
Walton called Layne's story "fanciful." He pointed out that she never complained to police about being attacked. A hospital nurse who examined her after her arrest said Layne had no injuries and spoke lovingly about Hoffman.
Sabbota asked jurors to view the incident through the eyes of a woman in her 70s. He said Layne was taking care of a teen who had used drugs and brought strangers to the home. Hoffman's parents were living in Arizona during his senior year of high school, and they had their hands full with a daughter being treated for a brain tumor.
After the verdicts were read, Sabbota said Layne has long been punishing herself and referred to her continued grief and regret.
"I've been saying it all along: We can't do anything that she hasn't already done to herself," Sabbota said. "She punishes herself every day. The legal system does what the legal system does. The jury felt that it wasn't appropriate self-defense. "