Sims comes from a Southern "old money" family and faced some prejudice when she joined the Navy. Her mother was particularly displeased with her career choice and decision to marry "a man named after a dog" – namely, Bud.
Sims first appeared in the second season episode "Crossing the Line" as an Ensign aboard Seahawk, where she had replaced her future husband, Lt. Bud Roberts, who was the ship's public affairs officer. Later in the season she transferred to JAG headquarters, attached to the administrative staff, and began a relationship with Roberts. Despite some last minute second thoughts, Sims marries Roberts in the penultimate episode of the third season. While Navy regulations strictly forbade fraternization, Admiral Chegwidden managed to pull some strings and has Sims transferred to the department of the Inspector General while remaining attached to the JAG headquarters administrative staff. Harriet is promoted to Lieutenant in the episode lifeline.