Before the American Civil War, military nursing in the United States was dominated by men and was not viewed as a good career for women.

After eighteen months, she was put in charge of a ward of fifty wounded Union soldiers at Fort Schuyler Military Hospital on Long Island in October 1862.

For two months, she performed nursing duties at Ft. Schuyler, sending letters back home that would later be published posthumously as her memoir.

In her letters, she tells of preparing men for amputations and sometimes death while snow and rain poured in through the slats of the hospital roof, and the wind rocked the building outside.

At Vicksburg, Mississippi, four hundred invalid soldiers were brought on board the ship, most of them sick with fever, many of them past recovery, and returned as far as Memphis, Tennessee.

From the steamship, Parsons again sent letters home, writing of the clouds of exploding shells being fired back and forth between the Union and Confederate armies.

At Memphis, after the sick and wounded had been transferred to the hospitals, an order was received from General Ulysses S. Grant to load the boat with active soldiers and return immediately to Vicksburg.

"There is too much a feeling among many here that they must be treated like inferior beings," she says, "They are only inferior from neglect, that is, I hope I can see my way clear to do my duty by them and all.” As supervising nurse, she also spoke with women of the Colored Ladies Aid Society who had to fight for the right to sit on the street cars that travelled to the wounded black soldiers' hospital and told her "things that would make your blood boil."

Though her decline in health eventually caused her to return to Cambridge, she continued to send boxes of gardening seeds and clothing to the freedmen and refugees at Barracks Hospital, so they could begin a new life in Missouri.

Her work has been cited along with writings by Clara Barton, Susie Taylor and Louisa May Alcott as one of the few memoirs available to researchers on the daily lives of the 3,000 women who served as military nurses during the American Civil War.