After having four sisters die as babies, Agnes came into the world very much wanted by her mother, father and five brothers. When she was one year old, her family moved into a yellow brick house in Blackfoot, Idaho, where she spent the rest of her life. She grew up in true ranch style, riding horses and driving cattle.

Agnes schooling went as far as the eighth grade, but after skipping High School, she went on to Albion Normal School in Albion, Idaho, and then on to Pocatello Academy to get her teaching certificate. She taught school at Cedar Creek for three years. It was here that she met her husband, Robert E. Reid, whom she married in 1906. They had five sons.

Even as a child, Agnes interest in writing had always been strong. By the time she was old enough to write, she was already writing short stories and poems. As she advanced in school, her talent became more noticeable. At sixteen years old, she sent her first verse to the Idaho Falls Times, but since poetry was not the popular thing at the time, she signed it "Sally." However, the poem was printed, and her career as a writer began.

Not only has she written many short stories and poems, she wrote a column in the Blackfoot newspaper, The Register, for quite a number of years. Many of her poems have been published in The Improvement Era, The Relief Society Magazine, the Salt Lake Tribune, the Deseret News, Utah Magazine, and the New West. Her best known writing is her book Letters of Long Ago, a biography of her mother, Emma Thompson Bennett Just, first published in 1923, and again in 1936 by Caxton Publishers of Caldwell, Idaho and a third edition was published through the Tanner Trust Fund.

Agnes was a great companion to all those who knew her. She was genuinely interested in people and her grandchildren found their grandmother easy to confide in. She made everyone feel at ease and was a comfort to be around.