Fabienne Kabou, 39, had faced life imprisonment for the November 19, 2013, murder, but the court deemed that she suffered from impaired judgement.
The court in the town of Saint-Omer, near Calais, also ordered Kabou to undergo psychological treatment as it wrapped up her headline-grabbing trial.
Her lawyer, Fabienne Roy-Nansion, expressed dismay over an "extremely heavy" verdict reached after the five-day trial and said Kabou planned to appeal.
The woman of Senegalese origin confessed to travelling from her home near Paris to the town of Berck on the English Channel with the aim of drowning Adelaide, who was 13 months old.
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Prawn fishermen found Adelaide's lifeless body the next morning.
Kabou, who grew up in a well-off Catholic family, left Senegal to study philosophy and architecture in Paris, where she fell in love with Michel Lafon, a sculptor 30 years her senior.
Described by her lawyer as highly intelligent, she told the court she had no other explanation for her acts but witchcraft.
"Nothing makes sense in this story. What interest could I have in tormenting myself, lying, killing my daughter?" she asked. "I spoke of sorcery and I am not joking. Even a stupid person would not do what I did."
She said she had spent some USD 45,000 consulting various "witchdoctors and healers" before carrying out the murder, and that she had suffered hallucinations.
However, a lawyer for a children's group that was a civil party to the case has accused Kabou of citing witchcraft and her native culture as a defence strategy.
An IT expert testified that he found no references to witchcraft on her computer.