Theophister Mukakibibi was sentenced by the traditional gacaca courts on Thursday for helping Hutu fighters to kill Tutsi hiding in a hospital where she worked. She was also accused of dumping a baby in a latrine.
Jean Baptiste Ndahumba, the president of the local gacaca court in Butare town, said: "She would select Tutsi [and] throw them out of the hospital for the militia to kill. She did not even spare pregnant mothers."
Mukakibibi is the first nun to be sentenced by a Rwandan court for her role in the genocide.
A Belgian court convicted two Roman Catholic nuns in 2001 for aiding in the mass murder.
More than 20 witnesses testified against Mukakibibi during the trial, which lasted over one year.
Ndahumba said: "She used to hold meetings with militiamen and had an army officer as her escort during the killings."
As the official in charge of stock in the hospital, she was also accused of denying food to Tutsi hiding in the hospital.
Roman Catholic church
The Rwandan Roman Catholic church is accused of playing a significant role in the 100-day genocide, in which an estimated 800,000 people were killed.
A Roman Catholic priest is on trial before a Tanzania-based UN tribunal, accused of odering the slaughter of 2,000 people who sought refuge in his church.
In July, 2005, the head of the Roman Catholic church appeared before a similar court to give information on what he knew about the genocide.
Thaddee Ntihinyurwa, the archbishop and a Hutu, was summoned to the local gacaca courts after dozens of survivors accused him of taking part in several meetings that were allegedly planning the slaughter of ethnic Tutsi in the southern Cyagungu province.
Focusing on confession and apology, the traditional gacaca courts have been used in Rwanda to ease the backlog of genocide cases.
They are also intended to ease the way to national reconciliation.
Under gacaca, those who confess and plead guilty before a set date will have their sentences reduced.
Those sentenced to prison will serve their time in a Rwandan jail.