Independent Complaints Directorate spokesman Moses Dlamini said the former commander of the Mtunzini police station, Lt-Col Zodwa Zulu, was sentenced by the Durban High Court on Friday.
She was also sentenced to two terms of imprisonment of eight years for attempted murder.
Zulu was convicted by the Vryheid High Court in February.
In September, after finishing work, Zulu drove to Nongoma where she shot and killed her sister-in-law.
“The accused also shot and injured her brother-in-law and shot at her mother-in-law,” Dlamini said in a statement.
“The accused started shooting at the victims through the window and went into the house through the broken window and continued shooting at the victims.”
The case was investigated by the ICD after Zulu handed herself in to the police.