The trial in Bobigny near Paris centres on Sabrina, a woman now aged 32, who was brought to a Paris hospital in March 2006 suffering from malnutrition and signs of torture.
Sabrina told police she had been tortured and held as a slave in a trailer park off the highway in Claye-Souilly near Paris.
She had lost nearly all of her teeth, her ears had been burned with a clothes iron, her body was scarred from cigarette burns and she weighed only 34 kilogrammes (75 pounds).
In December 2010 her parents, Daniel and Denise, were convicted of human trafficking for having allowed Sabrina to be sexually abused, including in exchange for a reduction on the price of a used car.
Her father was sentenced to 20 years in prison and her mother to eight years. The parents' last names have been withheld to prevent identification of Sabrina.
Another couple, Franck Franoux and his wife Florence Carrasco, were both sentenced to 30 years on charges of rape, kidnapping, torture and forced slavery in the case.
A verdict in the appeal is due on September 14.