Sidonia Perlstein survived the Holocaust to become a talented designer and seamstress. But when Perlstein died on Mother’s Day six years ago at the age of 93, she was still a mystery to the daughter she had raised alone in western Massachusetts.  “My real mother was someone I never truly knew,” said Hanna Perlstein Marcus.  But Sidonia’s death only made Marcus more determined to understand her mother and seek out the father about whom she would never speak.  Marcus recounts what she learned in her memoir, “Sidonia’s Thread: The Secrets of a Mother and Daughter Sewing a New Thread in America.”