Her name was Sarah Josepha (Buell) Hale. On September 28, 1863 with the approach of the Civil War, Sarah sent a letter to U. S. President Lincoln explaining her believed that a National Day of Thanksgiving would draw families and the nation closer together. At the time, she was editor of the famed Godey Ladies Magazine, and she encouraged her readers to write their own letters, effectively lobbying the president. President Lincoln declared the fourth Thursday of November as Thanksgiving Day, and it has continued to this day in the United States.
You can read the letter by Sarah Josepha Hale in her biography on WikiTree Bruell-648.
Happy Thanksgiving to those of you from the U.S., but we can all give thanks with a grateful heart - no matter where we live.
P.S. check the relationship finder. I just did and found out we are fifth cousins six times removed! ;-)