She was an active member of the Nebraska State Historical Society, serving for many years as its president, and wrote 13 books (primarily biographies) and many articles on Nebraska history, including biographies of her father, her mother, and Buffalo Bill Cody.

She suffered a childhood illness that permanently damaged her spine and slowed her growth resulting in her diminutive height of 4 feet,8 inches.

Harry fell ill and spent his last five years at the Grand Island Veterans Hospital.

During those years, as Nellie spent about 10 days out of each month at the hospital, she would sit by his bed side, writing manuscripts in long hand.

One of her most noted books, Buffalo Bill: His Family, Friends, Fame, Failures and Fortunes, was published in 1979.

It received excellent reviews, garnered awards, and resulted in a trip to New York to appear on Good Morning America on February 22, 1980.