Who is Hannah Armstrong from Spoon River Anthology and what is their importance?

Hannah Armstrong tells the reader she sent a couple of letters to President Abraham Lincoln, petitioning him to discharge her sick son from the Army. She says she received no response from the letters. Finally she went to the courthouse herself and told a guard to tell the President, "It's old Hannah Armstrong from Illinois." The President admitted her. They laughed and talked about old times, and then Lincoln discharged her boy from the Army.