Spears is serving a sentence of 20 years to life at the Bedford Hills Correctional Facility in Westchester County.
She was convicted of second-degree murder (guilty of depraved indifference murder of a child) in March 2015, a little over a year after Garnett's death.
"Shocking," Spears said of the verdict in the "48 hours" interview. "I did not murder my son. I did not hurt my son. And to be told that I was found guilty of murdering my own son, there are no words to describe that."
Prosecutors presented evidence that she forced him to overdose on salt through a feeding tube and Spears insists his death at Westchester Medical Center was a mystery.
Watch the "48 Hours" episode by clicking here.
Click here to follow Daily Voice Mount Pleasant and receive free news updates.