Twenty-eight-year-old China Arnold chose not to be in the courtroom for Monday's sentencing.
Arnold was convicted of aggravated murder in the 2005 death of month-old daughter Paris Talley.
She was spared the death penalty because jurors could not reach a consensus on the punishment.
It was Arnold's second trial; the first ended in a mistrial when new witnesses surfaced.
Defense attorney Jon Paul Rion has asked for a third trial, saying a former cellmate who said Arnold confessed has now changed her story.
The defense had argued that Arnold was drunk when the offense occurred and had no motive, while prosecutors had called the crime "heinous" as they argued for the death penalty.
During the trial, an 8-year-old boy said he saw another boy walk into the kitchen of a nearby apartment with the baby, heard the microwave go on and then later saw the burned baby in the microwave.