Swallow grew up on the world of Halcyon, where she used her looks to attract young men in bars, take them to her home, tie them up and flay the skin and meat from their bones with a fillet knife. She killed ten men in this manner before she was indentured into the military, her murderous impulses controlled via neural resocialization. The end result was that she was excessively perky and seemingly always smiling, her only remaining vice being a liking for cigarettes. She became very enthusiastic about serving in the military and combat.
When Universe News Network reporter Michael Liberty made some enemies amongst the Old Families, he boarded the Norad II to serve as a military reporter for Alpha Squadron. Colonel Edmund Duke ordered Swallow to serve as Liberty's "minder" – making sure he wasn't going anywhere he wasn't supposed to go, telling him when Duke wanted him, showing him around the ship, and other such duties. Liberty befriended her, however, even after he learned the reasons behind her resocialization. Even when she was ordered to throw Liberty into the brig for questioning Duke aggressively about the protoss attack on Chau Sara, Liberty remained her friend.
Swallow and Liberty traveled to Mar Sara after the destruction of its sister planet. Liberty was able to manipulate her into breaking the restrictions on foreign reporters on the world, which was under a military lockdown. He convinced her not to wear her powered armor as that would intimidate the locals as she drove him to various refugee camps to interview the people there. At one such camp they ran into a suspicious woman who argued with Swallow. Unable to deal with the stress, Swallow activated her stimpack in order to remain calm after they left. This woman turned out to be Lieutenant Sarah Kerrigan, who mentioned they would find the answers they sought "a few klicks" away.
On Kerrigan's advice, Swallow and Liberty traveled to Anthem Base, a seemingly abandoned settlement. They discovered some purposely mutilated human remains and then were attacked by xenomorphs. Swallow's high levels of fear and stress were sufficiently contained by the resocialization and stimpacks to allow her to fend off the zerglings. When the hydralisk arrived Liberty used the effects of resocialization and stimpacks to order her out of fear – or stress-induced inaction. The implication of zerg intelligence disturbed her further.
Having retreated into the local claims office Swallow fell into a pit and was attacked by more aliens. Her resocialization finally cracked and she was killed while screaming wildly and fighting with her combat knife. Only the upper half of her body remained intact.