Catherine Tissier, 40, had claimed that from the age of 14 until 27 she was forced to clean, wash and serve 15 hours per day, with no holidays or proper pay at a hotel school linked to Opus Dei.
A French court ruled there was no evidence she had been trapped all that time without remuneration.
She said as a "numerary assistant", she was forced to take vows of obedience, poverty and chastity and cut off from the outside world.
She had filed for charges of "concealed work" and "payment contrary to dignity".
Defence lawyers had insisted the trial, believed to be the first of its kind in Europe, was a simple labour dispute.