Not much is known about Leah's life prior to or as the outbreak began, except that she grew up in a dysfunctional family. As an adult, she joined a branch of the U.S. military and fought beside her squad, and they became like family to her. She also adopted a boy named Matthew after his mother died in childbirth.
Sometime after the outbreak, she met up with her squad and they survived for a year together until one day their camp was overrun. Leah took Matthew and fled the camp. She would later find out that he was bitten and put him out of his misery. The same day Matthew died, Dog was born.
Daryl stumbles upon some iron spikes protruding from a tree. Soon enough, Dog runs from out of the trees and beckons Daryl to follow him. The canine brings him to a nearby cabin. He busts inside an kills a walker, but is soon ambushed by a woman, who holds him at gunpoint. The woman asks for his name. Daryl attempts to leave, but the woman prevents him from doing so. Daryl sits tied up inside the cabin, as the woman drags the walker corpse outside. Daryl fiddles with his ropes, but is stopped by the woman. Daryl asks if she's going to kill him. She asks if she should, and believes Daryl doesn't want to die. Daryl spits back that she doesn't know anything about him, which she acknowledges, so asks for his name again, and why he is trespassing on her land. Daryl introduces himself and says that he was just trying to help, but Leah snarks that he is tied up with a shotgun pointed at his head, and rhetorically asks what kind of help could he possibly offer her. After a tense moment of silence, the woman decides to cut Daryl loose. Before he leaves, Daryl asks if she's going to tell him her name, but she tells him "no".
Six months later, Daryl is sitting at his shelter when he is startled by Dog. He takes Dog back to the cabin, where the woman thanks him for bringing her pet back. Since the woman still refuses to introduce herself, Daryl asks for the dog's name, but the woman simply calls him "Dog". The woman takes note of Daryl's scar, and says that living out in the wild isn't for everyone. Daryl supposes the lifestyle will catch up to all of them, but the woman replies that this will happen only if they let it. With that, Daryl takes his leave, and the woman tells him to be careful.
Eight months after this, Daryl is gathering some wood when he is ambushed by a group of walkers. He takes out a couple, but starts to retreat when he notices there are too many. Suddenly, the woman arrives to assist him and signals Daryl to follow her. They hide together and wait for the walkers to pass by. Once the threat has subsided, Daryl sternly tells the woman to stay away from his camp. Offended, the woman introduces herself as Leah as she leaves.
Three months after their encounter, Daryl arrives to the cabin and tosses a fish to Leah's doorstep. Sometime after Daryl returns to camp, Leah tosses the fish back at him, and says that she can catch her own. Daryl says that he was trying to be nice, but Leah asserts that she doesn't need him to be nice and just wants to be left alone. Daryl bitterly promises he won't bother her again, and Leah replies that she won't visit him either anymore. Noticing that she is still lingering, Daryl says that understands why she lives out in the woods by herself. Leah guesses that Daryl has been alone for a long time, too, which he affirms. Leah asks if Daryl has frostnip, but he brushes it off. Nonetheless, she invites him to spend the night at her cabin to get warm. Later that night, Daryl is woken to the sound of broken glass. He finds Leah picking up a broken picture frame. Leah explains that today is the birthday of the boy from the picture. She recounts how she didn't have a good family growing up, so she had to find her own. She fond that with her squad, with whom she fought side-by-side. When the world ended, they swore they would stay together. The squad, she says, gave her hope, and she tried to give the same to her son, Matthew. She tearfully admits that Matthew wasn't her biological son, but she adopted him after her close fried died giving birth to him. Tearfully, Leah laments that it doesn't matter, as Matthew is gone. She walks over to a window and looks over Matthew's grave. She continues her story, recounting how she was with Matthew and Dog's mother (who was pregnant) when the dead surrounded them. Leah was separated from her squad, and ran to the cabin with Matthew. It was only then that she noticed Matthew was bitten. Matthew died the same day Dog was born, which was the last time she saw another living person until Daryl. Leah asks him who he lost, so Daryl tells her it was his brother, who was lost in an accident but his body was never found. Leah asks if Daryl still thinks his brother is still alive, but he doesn't know, though promises to never stop looking until he finds out.
In the following ten months, Daryl and Leah spend a lot of time together, and even become romantically involved. Over time, however, Leah becomes increasingly frustrated with Daryl periodically leaving to look for Rick. One day, when Daryl reveals that he will be gone for a few days, Leah reaches her breaking point and asks Daryl where he belongs, whether it's by the river looking for his dead brother, with the family he left, or with her. Daryl claims he doesn't know, but Leah thinks he does, and tells him to choose. When Daryl comes back to the cabin, however, he finds it trashed and Leah missing, along with Matthew's picture. Dog, however, is still present, and soon joins Daryl. Daryl writes Leah a message saying "I belong with you. FIND ME.", and places it in a wooden box Leah kept under the floorboards, along with a few cans of food. He then leaves with Dog, telling his pet not to worry, as he is certain they will get Leah back.
Her ultimate location and fate remains unknown.
This list shows the victims Leah has killed:
- "Find Me" (Flashback)