Sallie's first battle came at Cedar Mountain in 1862. She steadfastly remained with the colors throughout the entire engagement. She did the same at Antietam, Fredericksburg, and Chancellorsville. No one ever thought of sending Sallie to the rear in time of combat. She was the regiment's spirit and its inspiration. During all battles she would race around the front line and bark ferociously at the enemy.

In a spring 1863 review of the Union army, Sallie marched alongside the 11th Pennsylvania. A tall man in the center of the reviewing stand saw the dog. With a twinkle in his eye, he raised his stovepipe hat in salute. Thus did Abraham Lincoln give a special acknowledgment to the mascot.

On the first day's fighting at Gettysburg, the 11th Pennsylvania was driven back from Oak Ridge and into town. During the chaos, Sallie became lost and three days later was found by a member of the 12th Mass. at the original position of her regiment when fighting broke out. Sallie had found her way back and was standing guard over the bodies of her dead compatriots. Neither hunger nor thirst swayed Sallie from her duty.

That following May at Spotsylvania, Sallie received a neck wound during the battle and proudly bore a "red badge of courage". On February 6, 1865, the 11th Pennsylvania made a concerted attack upon the rebel lines at Hatcher's Run. As always, Sallie was right at the end of the first line of attack. Men in the second wave were advancing under heavy fire and came upon the body of Sallie. She had been shot through the head and killed instantly. Under horrendous fire, the weeping men of the 11th Pennsylvania buried the little dog where she lay on the battlefield.