SAINT-JOSEPH, France—Declared dead by a French court in 2017, Jeanne Pouchain has spent the past four years trying to escape a bewildering legal twilight zone and prove to officialdom that she is in fact very much alive. She says the experience has been devastating. “My name was Jeanne. It still is Jeanne, after I’ve been declared dead in 2017,” says the 59-year old, smoking cigarette after cigarette. She breaks into tears at times when recounting her ordeal—and what she plans for when she will officially be “alive” again. It all started, Pouchain recalls, when the family received a letter four years ago from a court saying mistakenly that she was dead and that her husband and son had to pay for money she was alleged to have owed. The letter was part of a complicated legal procedure launched by a former employee of Pouchain’s cleaning business and, unlike what they …