Maria-Faustina spends her early childhood in Italy before her father decides to cross the Alps to look for a better life in France. He is a salesman and opens up a new business in the town of Thônes in Haute-Savoie.
Maria-Faustina, whose name has become Mariette in France, helps her father in the shop. She is a beautiful young woman, has a strong willed personality, and attracts many men. She gets involved in several relationships, gives birth to two children that she gives up for adoption, after keeping them hidden for a while.
Her life changes when she decides to become an actress. She is tempted by the high society life of Paris and marries Marquis of Thèze, whom she leaves soon after the wedding. She is quite an extraordinary person : she is one of the first women to drive a car. The Marquis decides to get back at her and has her arrested after the Second World War, claiming that she has been a spy. She is incarcerated in Nontron but uses her charm to talk her way out of jail. 
She ends up living alone in Lamalou-les-Bains in the province of Hérault. She has never received any artistic training but is able to master her own technique with creativity and freedom. The fear of deteriorating physically is ever present. Her story is described in a feverish and hallucinatory style. Her family says she was involved with spiritualism. Her production is restricted to about three hundred charcoal drawings, created over the course of one or two years, drawn on invoices from the Mobiloil gas station.
On Christmas 1970, she posted a note on her door saying : "Gone on a trip". A suspicious neighbor had her door knocked down and found the Marquise in the state of extreme weakness, surrounded by frescoes covering the walls of her apartment in the same style as her small drawings. She died in the hospital a few days later.