Lynn was one of the Dauntless-born initiates who made it through the initiation.
At first, the only thing Tris Prior notices in Lynn is her shaved head. However, when her hair grows back a bit, Tris realizes how pretty Lynn actually is, saying that she's "striking without trying to be". She has golden-brown eyes, a delicate nose and full lips, with an eyebrow piercing. During initiation, she has shaved her hair and started to dress in clothes that hide her curvy figure, because the Dauntless boys didn't see her as a threat because she's a girl. Lynn most likely isn't tall, since she's described as being only a few inches taller than Tris. She has a tough attitude and a mischievous sense of humor.
Lynn comes off as blunt and rough around the edges to Tris during their first introduction. It was revealed that Lynn sought to prove herself to her fellow Dauntless from a young age, resorting to her hiding her feminine features behind loose clothes and a shaved head.
As demonstrated in Insurgent when confronted with the Dauntless under Eric's command, Lynn is not the 'forgive and forget' type, instead viewing the latter as a traitor for his actions.
Underneath her tough exterior, Lynn has shown she cares for the welfare of her friends and family, especially her younger brother Hector.
Lynn is first introduced as the Dauntless who stomps on Tris's foot prior to ziplining. She treats Tris indifferently until later in the initiation process when the latter begins to show improvement in the rankings. Prior to the first session of the fear simulations, Lynn sizes up the transfers and replies that she is probably better than the person currently ranked first (Peter). This prompts Will to object to Lynn's attitude and he fires back that she has an advantage growing up Dauntless. However, Lynn replies that no one can prepare for the fear portion of the initiation. When Tris excels at the fear portion of initiation, Lynn along with Uriah and Marlene congratulate Tris, noting that someone should do so when the others (Will and Christina) are treating Tris coldly. Lynn ranked second in the group of Dauntless-born initiates at the end of Stage One.
Lynn and Tris are better acquainted in Insurgent. The two become friends and Lynn helps Tris after she moves to the Candor headquarters. She shoots Max while spying on him during his rendezvous with Jack Kang. Lynn blamed herself for her sister's paralyzing injury that happened in the aftermath of the fatal shooting. Later, she snaps at her best friends Marlene and Uriah Pedrad about their relationship and tells them that they should just kiss already. When the two finally kiss, she seems a little bitter. Toward the end of the book, she is found fatally wounded by a bullet and dies while being comforted by Uriah and Tris. She admits that she loved Marlene more than a friend right before she dies, which explains a few things mentioned prior to her death.
Lynn is one of the Dauntless who greets Tobias and Tris when they regroup at the Candor headquarters. She and the others are knocked unconscious when Eric infiltrates Candor and injects everyone with a new version of the serum. Once she comes to, Lynn grumbles about being taken out so easily and mutters about the strange metal pellet fired at her, which resembles a small metal disc. She snaps at Hector to stop picking at his.
Lynn witnesses Marlene falling to her death under the simulation at the Factionless headquarters. When Evelyn comments about the victims in the apparent suicide, glossing over Marlene's name, Lynn speaks up and remarks "Marlene. Her name was Marlene." while glaring at Evelyn.
At the end, she and the Dauntless invade Erudite to find Tobias and Tris.
Lynn had a close relationship with her siblings Shauna and Hector. She tended to boss Hector around but did so for his own good.
She was also very close with Marlene and Uriah, although she seemed unhappy and bitter when they started a romantic relationship. It was revealed in Insurgent that it was due to the fact she was in love with Marlene. She never told Marlene before Marlene was killed in the simulation, but tells Uriah and Tris that she loved her before she dies.
Although she appeared to be brusque and sarcastic toward Tris in Divergent, Lynn sides with Tris in Insurgent, defending her from the others who believe Divergence is dangerous. When Tris saves her younger brother Hector from committing suicide under a simulation, Lynn privately thanks Tris.
During the aftermath of the Dauntless invasion on Erudite Headquarters, Lynn is shot in the stomach and brought up to the main hall. Uriah does get a medic, but it is confirmed that it is too late to save her, as the hospital had been burned down from the attack. Lynn maintains her normal sarcastic attitude, saying "Uri, shut up. It's too late". Before Lynn dies, she tells Uriah and Tris that she knew Uriah was in love with Marlene and she loved her too. It is implied or hinted that Lynn cared for Marlene in a romantic way versus platonic, based on her delivery of her last sentence. She closes her eyes and dies a few minutes later.