Followingg a two-week appeal hearing in Puy-en-Velay, an all-woman jury found the pair guilty of the murder of the blonde, blue-eyed five-year-old.
In May 2013 Bourgeon, now 30, appealed for help in finding her daughter, saying she had disappeared from a park, but four months later she and Makhlouf, 36, admitted they had buried her in a forest, claiming she had died in an accident at home.
In 2016 a court found Makhlouf guilty of the murder, sentencing him to 20 years, but not Bourgeon, although it jailed her for five years for lying about the killing.
The appeal court found both guilty of murder, although the body has never been found.
Prosecutor Raphael Gentile de Sanesi described the couple as a pair of "torturers", who had collaborated in the "continuous violence" suffered by the child during "the days and hours leading to her death".
The various contradictory stories put forward by the defendants, who both accused each other of brutality towards Fiona, were "not enough to give rise to reasonable doubt", the judgement declared.
It withdrew Bourgeon's authority over her two other children.
Her lawyers said they would appeal to a higher court.
"She got the sentence she deserves. It is relief for me and justice for Fiona," the girl's father, Nicolas Chafoulais, said. "But am I at peace? No.
"It hasn't brought my daughter back."