Enid Zentelis thought she knew everything about her grandmother, Bella Vital-Tihanyi — a Hungarian Holocaust survivor, mother of two and late-in-life avowed nudist who died in 1998. “She was my rock,” said Zentelis, who traveled the world with Bella and even lived with her for a time. Zentelis believed that Bella, born in 1915, had a straightforward war story. A neighbor turned in Bella as a Jew, and she spent several months in a Budapest prison. She survived the Nazi regime thanks to fake papers claiming she was a Swedish citizen waiting to go home. But Zentelis’ view changed in...