In Mockingjay, Leeg 1 was a soldier fighting in the rebellion from District 13. She is a young woman, possibly in her twenties, who, along with her sister, served under Commander Boggs in Squad 451. The sisters look so similar in appearance to one another while in uniform that they are referred to as Leeg 1 and Leeg 2 by the Squad for clarity. Katniss admits that she has difficulty telling them apart, until she notices that Leeg 1 has "weird yellow flecks in her eyes". While she is mentioned as Leeg 1, it is not her real name. This is because Katniss never remembered Leeg 1 and Leeg 2's real names.
Leeg 1 journeys to the Capitol along with her squad to fight in the final battles of the war, which will finally put an end to President Snow's bloody regime. Once they arrive, Leeg 1, like other members of her squad, is disappointed to learn that Squad 451 isn't really expected to participate in any real battles. They are informed by Cressida that they are part of the "disinformation team" that is designed to distract the Capitol from the rebels true purpose, disabling the pods so that they may advance safely into the Capitol. They were referred to as the "Star Squad".
On the fourth morning, Leeg 2 hits a pod that has been mislabeled and is killed instantly by a dart to the brain. Following her sister's death, Leeg 1 breaks down in tears one night in the soldier's encampment from grief. Shortly thereafter, she participates in a propo that is being filmed for the rebellion. The propo, while complicated, isn't expected to be very dangerous. The propo, however, goes drastically awry when Boggs accidentally detonates a land mine hidden under some paving stones. She seems to care a lot about Boggs, since she requests to take Boggs with them. The bomb sets off a chain of events that forces the squad to retreat into an abandoned apartment where Katniss lies when she informs the squad that she is on a "special mission" to assassinate President Snow.
Initially, the squad argues over the validity of Katniss' statement, but when Cressida backs up the lie, it puts a stop to the squabbling. Leeg 1 and the rest of the squad decide to continue on to help Katniss fulfill her mission. It is eventually determined that the squad must journey underground if they hope to achieve their objective.
Everything seems to be moving smoothly until the squad realizes that they are being pursued by a group of reptilian muttations through the Transfer. During a shootout with a group of Peacekeepers who are eventually decapitated by the muttations, Leeg 1 stays behind along with Jackson to hold the mutts off while the rest of the squad makes it to safety. The exact manner of her death is not explicitly stated, but it is left to the reader to assume that Leeg 1 was either killed by the Meat Grinder or was decapitated by the lizard mutts.
When the building that Squad 451 was inside explodes, the Squad is thought to be dead. Leeg 1 says, "My father. He just lost my sister and now..." This statement tells us she has a living father who most likely lives in District 13.
In the film adaptation, Leeg 1 decides to take care of Leeg 2 in an abandoned building while the rest of Squad 451 departs. Soon after, Peacekeepers attack the building, with the Leegs shooting back. The Peacekeepers' response ends blowing up the building, and the destruction footage is used by the Capitol to imply Katniss has died.