In 1856, in their home in Cambridge, Agassiz founded a school for girls from Boston. Her husband supported her by giving courses as well as arranging for courses from other Harvard professors. After the closure of the school in 1863 she helped organize and manage The Thayer Expedition with her husband, who she accompanied to Brazil (1865–1866). This expedition, occurring from 1865–1866, came at the end of the American Civil War, its maiden voyage from New York to Rio de Janeiro beginning in the war's final week. In 1867, she began a correspondence with Arnold Guyot, a geologist and meteorologist. She also helped organize and manage the next expedition (the Hassler Expedition in 1871-1872), which was the first important U.S. government marine exploration, and made transcripts. After her husband's death in 1873, she published several books on natural history for which she had conducted research for many years.