Gruber was born, she says, in a shtetl. However, her shtetl wasn't a tiny village in Russia or Poland, but rather the Williamsburg section of Brooklyn, New York. "On Moore Street," she says of her birth home, "I thought the whole world was Jewish. The butcher, the grocer, the dressmaker, the corsetiere who made my mother's corsets - everyone was Jewish." The Brooklyn of Gruber's birth in 1911 was growing quickly, filling with recent arrivals to America. Her own parents had both been born in Eastern Europe, her father coming to America only in 1901. Both sides of her family kept close ties to relatives they'd left behind in Europe, and all her life, foreign affairs and family affairs would mix.
Though Moore Street was predominantly Jewish, Gruber could find a variety of cultures just beyond her door. "Brooklyn was like a little Europe then," she says. "There was a Jewish section, a German section, an Italian section, an Irish section, and the Gypsies wandered through it all." Moving from neighborhood to neighborhood was like passing from nation to nation, an environment that gave Gruber easy access to different languages. She grew up speaking not just English but Yiddish, and she soon learned its close cousin, German, as well. A precocious student, she graduated from high school at age fourteen, and received her bachelor's degree from New York University at eighteen.