Probate Judge Margaret Noe opted to sentence Adkins as an adult. She could have placed her in a juvenile facility until age 21 and then evaluated whether prison should be appropriate, court administrator David Stanifer said.
"She was very emotional and was crying," Stanifer said of Adkins. "I think she realized some serious consequences were going to hit."
"The judge received numerous letters from family members, both supporting a light sentence and a very severe sentence," Stanifer said.
Adkins pleaded guilty to second-degree murder on Oct. 10. Her attorney, Mike McFarland, claims she was mistreated by Bentley, 53.
McFarland told the court that Adkins had a troubled childhood that included mental health problems and drug abuse by the time she was 13, according to The Daily Telegram of Adrian.
McFarland said Adkins never gave a specific explanation for why she wanted to kill her grandmother. "I think it was cumulative of her entire life experience," he said.
Lenawee County is on the Michigan-Ohio border.