John Harvey Kellogg and in 1898 released the first batch of Sanitas Toasted Corn Flakes. A modified version with a longer shelf life was released in 1902. By that time, both "Granose Biscuits" and "Granose Flakes" were available. Will Kellogg continued to develop and market flaked cereal. When he proposed adding sugar to the flakes, John would not agree to the change. So, in 1906, Will started his own company, the Battle Creek Toasted Corn Flake Company. This marked the start of a decades-long feud between the brothers. Will's Battle Creek Toasted Corn Flake Company would eventually became the Kellogg Company, while John
Fay Kellogg death in 1901, Kellogg set up business for herself, establishing her own office in 1903. One of her first commissions was the renovation and construction of seven buildings on Park Place in Manhattan for the American News Company. She was soon in charge of all their building and renovation work in the United States. For jobs within 200 miles of New York City, Kellogg would supervise directly. For projects further afield, she would draw plans. Kellogg also helped design the Woman's Memorial Hospital in Brooklyn, founded by female physicians in 1881, as well as hundreds of other buildings and cottages.