The incident took place yesterday in Rugomero village, Nyaruteja cell where she lived with parents.
Hagenimana was a senior 3 student.
One of the residents said the lady had spent three weeks in the village after returning pregnant from Kigali.
“The girl went to Kigali after her senior 3 examinations. She had spent only three weeks in the village from the time she returned being pregnant,” she said.
The executive secretary of Nyanza sector, Jean Baptiste Kayinamura said they were alerted by residents.
“We immediately went to the crime scene after a tip-off from residents and found the baby in the toilet, dead. The girl admitted to having dumped the baby after delivery,” he said.
Police spokesperson in Southern province, CIP Sylvestre Twajamahoro said the girl was arrested and detained at Rwanda Investigation Bureau station in Nyanza sector.
The baby was taken at the University Teaching Hospital of Butare (CHUB) for postmortem.