The 15-month-old's dead body was found by fishermen the next morning.
Investigators tracked Fabienne Kabou down using CCTV in a northern seaside town. She is believed to be suffering from hallucinations and depression.
She said: "I put an end to her life because it was easier that way. It was as if I felt carried along, I just couldn't say stop."
According to court documents, the baby's father, Michel Lafon, did not take an interest in his child.
She was given the name Adelaide but was never officially registered, and nobody apart from the couple knew of her existence.
In November 2013 Ms Kabou travelled from her home in Paris to the town of Berck-sur-mer where she asked local people about the tide times, then left the baby near the water.
She has at times said she left her daughter there because it caused difficulties in her relationship with the baby's father. At other times she has said she was influenced by hallucinations and witchcraft.
One psychologist said her background of growing up in Senegal had given her "an individual history linked to witchcraft" in the West African country, and "radically altered her view of the world".
Her lawyer said before the start of the trial that Ms Kabou "sees her act as we all see it, that is to say, something utterly horrible, and she considers herself indefensible".
A woman has gone on trial in France for leaving her infant daughter on a beach to die on a cold November night.