Leggett was born on May 9, 1815, in New York City, at 90 (later 21) Beekman Street to parents Valentine Seaman and Anna Ferris.

Her father died in 1817, and she (the youngest of ten children) was the last child still living in the family home.

[1] Their home served as a stop on the Underground Railroad, and was also visited by many Progressives, including Amos Bronson Alcott, Julia Ward Howe and Sojourner Truth.

[3] She knew and corresponded with many authors, including William Ellery Channing, Washington Irving, Theodore Parker, Amos Bronson Alcott, Charles A. Dana, William Cullen Bryant, Walt Whitman, Louisa May Alcott, Ralph Waldo Emerson and Lucretia Mott.

Leggett also worked with Helen Eliza Benson Lloyd Garrison, Lyman Beecher, Laura Smith Haviland, and Elizabeth Comstock.