Albert Einstein had a sister named Maria. Nicknamed "Maja," Maria was two years younger than Albert and was born Nov. 18, 1881. Wikipedia lists Maja as Albert Einstein's only childhood friend.
Maja Einstein studied romance languages and literature at schools in Berlin, Paris and finally at the University of Bern, where she graduated in 1909. She married Paul Winteler in 1910 and lived with him in Luzern and then in Colonnata, just outside Florence in Italy. They had no children. In 1939, Maja emigrated to New Jersey although her husband was refused entry due to health reasons. Maja died of atherosclerosis on June 25, 1951, just four years before the death of her brother. She was 69 at the time of her death.