Horowitz was the daughter of Jacob Yokl ben Meir Ha-Levi Horowitz (1680–1755) and Reyzel bat Heshl. Her father was a member of the famed kloiz of Brody. Horowitz was one of some seven children. Three of her brothers were rabbis, of whom the most eminent was Isaac (known as “Itsikl Hamburger,” 1715–1767), rabbi of Hamburg, Altona, and Wandsbeck. There was also a sister, named Pessil. There is some doubt about the identity of another brother and sister. As the sister of eminent brothers, Leah disproves the old canard that the only educated women in her time were the daughters of learned rabbis who had no sons.