Police arrested Lucero Oscava Burgos, 21, in Puno, southern Peru, after the tot’s father Marco Antonio Ticona Chiccalla claimed she had killed his daughter.
Burgos initially claimed the baby had died after falling out of bed and admitted burying the body by the river Hatun Mayu on February 7.
Police cordoned off the area and carried out a search but were unable to find the child’s remains.
When they returned to question the mum, she admitted to suffocating her baby with a blanket before burning the body and dumping it in a grain silo, local media report.
Burgos was supposedly driven to murder after discovering her husband had been cheating with a workmate.
Police returned to the scene and found the girl’s wrapped in blankets and partially burned.
The child’s remains have been sent for an autopsy while the mum remains in police custody as the investigation continues.