Zorana Banic, 51, was found guilty of taking part in the executions of 43 Croatian civilians in November 1991 during the Croatian-Serbian war in the village of Skabrnja near Zadar.
It was the third time that the same Croatian court sentenced Banic for the same war crimes, after first being sentenced to 20 years in absentia in 1998.
After being arrested in Switzerland in 2001 and extradited to Croatia, to Zadar, she got a fresh trial in 2002.
At the end of that trial, she was again found guilty and sentenced to 13 years in jail.
But the Croatian Supreme Court this January overruled the sentence and ordered a retrial because her case contained "abnormalities and contradictions".
Her third trial which ended on Thursday had begun in March.
Banic, a former member of Croatian Serb paramilitary forces, insisted she was innocent and is still seeking to be extradited to The Hague-based International Criminal Tribunal for the former Yugoslavia (ICTY).
The Organisation for Security and Cooperation in Europe (OSCE) mission to Croatia has said earlier this year that the Croatian judiciary "has problems" in conducting war crimes trials.