The grisly find was made by her former husband when he defrosted the freezer in the house where they used to live, said prosecutors in the northern city of Flensburg.
It was not clear whether the baby was alive or dead when placed in the freezer, investigators said.
There were no signs she had been violently treated but authorities confirmed the baby was not stillborn.
The woman, who has not been named, has admitted the baby was hers and said she was “in a state of complete exhaustion and hopelessness” at the time.
The couple already had three, now fully grown, children and divorced in 2009, prosecutors said.
The woman was released pending further investigations.