The woman kidnapped the girl after she finished school. In an apartment, she then subjected the girl to severe torture and rape before murdering her.
In the verdict, which fell on Friday, the judge referred to the "extreme cruelty of the crime" and described it as "pure torture" and "total dehumanization".
The sentence – life imprisonment without the possibility of parole – is the most severe in French law. It is the first time a woman is sentenced to this punishment.
"When determining a suitable sentence, the court took into account the enormous psychological damage inflicted on the victim and her family under these violent and almost indescribable circumstances," said the judge.
The crime has become a focal point in the French debate on immigration because the woman, who is of Algerian origin, had not left France although her student visa had expired.
