In 2267, in this capacity, she was dispatched to Epsilon Canaris III to prevent the outbreak of war. Her mission was interrupted when she contracted Sakuro's Disease, an extremely rare illness that was fatal if left untreated.
She was extremely bitter about her recall, blaming her illness on the incompetence of Starfleet's medical branch. She believed she should have been properly inoculated, despite Doctor McCoy's statement that the odds against developing Sakuro's Disease were literally billions to one.
The USS Enterprise sent a shuttlecraft to retrieve the commissioner so that she could be ferried back to the ship's sickbay for a cure. En route to the starship, an alien called the Companion seized control of the shuttlecraft, diverting it to a small planetoid in the Gamma Canaris region. This posed a problem because, while Sakuro's Disease was curable in a medical facility, it was guaranteed to be fatal outside of such a facility. Marooned, Nancy Hedford faced certain death.
Living on the planetoid was Zefram Cochrane, inventor of the warp drive, and the Companion. Cochrane "felt" to the Companion a need for more Human companionship. He hoped the alien would free him to seek this elsewhere, but instead it brought nearby Humans to it.
Various attempts to persuade the Companion to cure Nancy Hedford, or to free its Human charges all failed, until Captain Kirk realized it was in love with Cochrane, and presented its differences as an eternal barrier to that love; he hoped this would at last convince the alien to free the Humans – love expressed as sacrifice. Instead, the Companion elected to merge with Nancy Hedford, who was moments from succumbing to her illness. To do this, the creature abandoned its immortality and its suite of powers.
Nancy Hedford was played by actress Elinor Donahue.
Elinor Donahue found that Commissioner Hedford turned out to be one of her favorite roles. "I do remember the experience as being very positive," she noted. One aspect that made the experience enjoyable for her was that the episode's director, Ralph Senensky, was very capable of telling actors how he wanted them to play their parts. "I felt very grateful for that," the actress admitted, "because it's always good to have one director around instead of four or five." (Starlog #130, p. 74)
The on-screen portrayal of Nancy Hedford was also influenced by Elinor Donahue's body weight. "After a few days, I was honored to be asked to share with them [i.e., the cast] their specially prepared diet barbecued lunches. As a result, I lost weight and the costumer fashioned gauze drape around my head and chest to disguise my boniness." (Starlog #130, p. 74)
Hedford was described in the final draft of the script as "a very beautiful woman in her early thirties, but one whose beauty is marred by the slightly sullen, annoyed look on her face. We should get the impression, from her attitude and appearance, that despite her beauty she is not particularly a pleasant person to be around."
The character's full name ("Nancy Hedford") appears in the script and end credits, but her first name, "Nancy," was not spoken aloud in the actual episode.