Twisted China Arnold intentionally put her helpless 28-day-old child, Paris Talley during a drunken argument about whether the boyfriend was the infants biological father.
Dr. Marcella Fierro, retired chief medical examiner for Virginia testified the baby was in the microwave for more than two minutes.
She said: "She died because she was overheated. She was cooked."
Two psychologists also testified that Arnold was of average intelligence and showed no signs of serious mental illness.
Dr. Jeffrey Smalldon said Arnold suffered from a "low-grade chronic depressive condition" as well as alcohol and drug abuse.
He added that he found nothing "that would have justified the death of this child."
It was Arnold's third trial in her daughter's 2005 death. Her first trial ended in a mistrial when new witnesses surfaced just before closing arguments. Her second trial ended in a guilty
verdict and a life sentence. But an appeals court overturned the conviction when it found prosecutorial misconduct and that the trial judge erred in not allowing a relevant witness to testify.
An investigator close to the case said: "Paris Talley was a helpless child who did not deserve to die at all, let alone in such a terrible manner.
"We're all glad to see justice has finally been served on this case which has been traumatic for everyone who worked on it."