The infant's body was found when a Flensburg-area man was defrosting the freezer last week, Suddeutsche Zeitung reported Tuesday.
The woman, reportedly the man's former wife, confessed to placing the baby girl in the freezer, police said.
The child was described as a "full-term infant," not a stillborn, prosecutors said. Police said they were investigating whether the girl was alive when she was put in the freezer.
Police said the woman, 49, confessed to killing her baby, saying she was feeling exhaustion and hopelessness, Suddeutsche Zeitung said. The woman said she and her husband already had three children and that she did not think she could raise another child.
Officials said the man told investigators the freezer had been used mainly by women.