 Gertrude was born in New York on May 12, 1842.She was the youngest of seven children born to Bernard Rhinelander (1800–1844) and Nancy Elizabeth Mary (née Post) Rhinelander (1806–1895) and was descended from a family that had resided in New York City since the 17th century.Her older siblings included Charles Edward Rhinelander, who married Mathilda Frances Cotheal; Emily Rhinelander, who married Dr. John Watson; and Laura Virginia Rhinelander, who did not marry.