Jennifer Hailey first caught the attention of Major Samantha Carter as a Cadet in the Air Force Academy. After Carter's lecture on Theoretical Astrophysics, Hailey approached the whiteboard and correctly pointed out a flaw in a complex equation. Carter quickly found out Hailey had disciplinary problems and recognizing the Cadet's potential, Carter took Hailey under her wing.
Jennifer's problems with authority stemed from her brilliance. She attended the Air Force Academy looking for a challenge of some sort but finding none, she became bored. Rather than complete assignments given to her, she decided to write her own papers, including one titled: "Towards a New Cosmology of Multiple Realities." Though an intriguing term paper, it was given a "D" grade because the paper she wrote was not the assignment given. Carter read the paper and likewise found it intriguing, yet critiqued it as being based on too many unfounded assumptions, including the theory that matter can travel both ways through an open wormhole, a theory Carter knew to be incorrect given her work at Stargate Command.
Nonetheless, Cadet Hailey was preoccupied with being correct at all costs and was even unwilling to listen to the opinions of others. In addition, she was also hot tempered, going as far as breaking a male Cadet's nose in a conflict which led to her superiors writing her off and deeming her to be expelled.
Given her attitude and state of mind, she was unable to see the possibilities ahead of her. Carter intervened, saving Hailey from expulsion from the Academy and decided the best possible way to steer her on the right path was to give her a glimpse of her possible future: the Stargate.
Jennifer traveled to the moon designated M4C-862 with Carter, where she was met at the gate by Colonel Jack O'Neill. After a bit of exploring and a discussion with Teal'c, she, and the rest of the expedition, were attacked by a swarm of Small energy beings. Carter's theory was that the behavior of these creatures was a retaliatory one for keeping one of the creatures captive in a sort of magnetic cage. However, Hailey's theory was that their behavior coincided with the moon's orbit passing over one of the nearby gas giant's poles.
Still putting too much importance on being right, she was quickly put in her place by both O'Neill and Carter. O'Neill decided to risk his life to save the expedition, rather than wait to prove Hailey's theory. The experience was a very humbling one for Hailey, and with the knowledge of traveling to other planets (and moons) in her future, she gained a better attitude, graduated the academy, and was accepted as a recruit into the SGC. (SG1: "Prodigy")
A year later, in 2002, Hailey, having been commissioned as a lieutenant, participated in a training exercise alongside Lt. Kevin Elliot, Lt. Carl Grogan and Lt. Satterfield. Posing as a fellow trainee, she pretended to be incapacitated in order to test Elliot's commitment to his fellow team members. She later told Elliot that his test was nothing compared to what the SGC had put her through during her own training. She was eventually assigned to an SG Team. (SG1: "Proving Ground")
As of 2010, Hailey is a Major serving as chief science officer on the George Hammond under Colonel Carter. It is mentioned that she served at the SGC until 2005, when she transferred to Area 51 at the same time as then-Lieutenant Colonel Carter took over as commanding officer of Research and Development. She spent the next few years working on Earth's BC-304 fleet, before being permanently assigned to the Hammond. (SG1: "Sun-Breaker")