Edmonds' career as Frank Thompson came to an end when she took a trip to Berry's Brigade in order to deliver mail to Union forces. In an attempt to take a shortcut, she was thrown into a ditch by her mule before reaching the brigade; she sustained severe injuries and could not finish the trip before the First Battle of Bull Run had commenced. She abandoned her duty in the military, fearing that she would be discovered if she went to a military hospital. She checked herself into a private hospital, intending to return to military life once she had recuperated. Once she recovered, however, she saw posters listing Frank Thompson as a deserter. Rather than return to the army under another alias or as Frank Thompson, risking execution for desertion, she decided to serve as a female nurse at a Washington, D.C. hospital for wounded soldiers run by the United States Christian Commission. There was speculation that Edmonds may have deserted because of John Reid being discharged months earlier, and there is evidence in his diary that she had mentioned leaving before she had contracted malaria. Her fellow soldiers spoke highly of her military service, and even after her disguise was discovered, they considered her a good soldier. She was referred to as a fearless soldier and was active in every battle that her regiment faced.