There is not enough information contained in the article but I would have liked to have been in on the investigation. I have not seen defense used as a defense in my area.

PONTIAC, Mich. (AP) An 75-year-old woman "hunted down" her teenage grandson in her suburban Detroit home and shot at him 10 times over a six-minute span, even ignoring his desperate pleas for help to a 911 dispatcher, a prosecutor told jurors Monday, urging them to convict her of first-degree murder.

Summing up his case against Sandra Layne, prosecutor Paul Walton again played 17-year-oldJonathan Hoffman's 911 call last May in which he said his grandmother had just shot him. "I'm going to die," he said before he was shot again with the dispatcher on the line.
There is no dispute that Layne fired the shots in her West Bloomfield Township home, striking her grandson six times. The question for jurors: Should she be held criminally responsible for Hoffman's death and, if so, how?
The options are first-degree murder, second-degree murder, voluntary manslaughter, involuntary manslaughter or acquittal based on self-defense.
Layne testified last week that she was afraid of her grandson and acted in self-defense. She said she shot him after he struck her while arguing over his demands for money and a plan to flee Michigan. Hoffman had failed a drug test earlier that day, which could have been a parole violation.
Walton reminded jurors that Layne didn't report any injuries to police when they arrived at her home after the shooting.

Prosecutor: Grandma 'hunted down' teen grandson - Yahoo! News