Lianne was the high school sweetheart of the future millionaire, Jake Kane. Lianne and Jake both attended Neptune High, where Lianne was credited with being both a gossip and a friend to the deaf girl, Mary Mooney (biological mother of Trina Echolls). Lianne later marries Keith Mars. Despite her marriage to Keith, Veronica's paternity is at one point under question--it being unclear if Keith or Jake is her father., Keith eventually proves that he is indeed Veronica's biological father. After the Lilly Kane murder is made public, Lianne left the Mars family for parts unknown.
Veronica tracks her mother down during her junior year. Lianne claims to want to fix her problems so Veronica, ever eager to help and still wanting to get her family back together, cashes in all of her college savings to put Lianne into rehab. Afterwards, Lianne returns to stay, seemingly sober. It turns out, however, that Lianne is still drinking, and Veronica confronts her.
- VERONICA: I know, Mom. I know you're not through drinking, I know you didn't even finish rehab. You checked yourself out and that was my college money. I bet on you, and I lost. I've been doing that my whole life. And I'm through.
With that, Veronica tells Lianne to pack her bags and leave. Lianne does so, but not before stealing the reward Keith had earned for locating the runaway Duncan Kane, leaving the remaining Mars members in a dire financial situation and Veronica again with no college money.
Years later, while discussing the Hayley Dewalt missing persons case with her father, Veronica spots a report on television involving a second spring break kidnapping, this time a girl named Aurora Scott whom Veronica had briefly seen at a party the night before. She and Keith are shocked to see Lianne on the television publicly pleading for the return of her step-daughter.
Veronica, who is working on Hayley's disappearance, visits Lianne to question her about Aurora's disappearance. Though initially taken aback by her daughter's sudden appearance, she is not completely surprised. Lianne briefly interrupts the interview to tell to Veronica about the last seven years of her life, her husband and their son (Veronica's half-brother) as well as her own sobriety.
Tanner is shown to be very familiar with Veronica and is quite welcoming of her to their home. The interview continues awkwardly and though Lianne and Veronica part without a hug, Veronica promises Lianne to find her daughter for her.
As the cases advance and a ransom demand is made, the body of Hayley Dewalt is recovered by Veronica who deduces that her ex-boyfriend, Chad Cohan, was guilty of the murder. However, because Aurora has no connection with that lovers' quarrel, it becomes clear that the crimes are separate incidents.
A revelation is made when Veronica discovers Lee Jackson, a man Tanner Scott had specifically asked to act as their consultant in dealing with the ransom demands, is actually a man named Duane Shepherd. Veronica confronts her mother with an accusation toward Tanner, who is arrested and confesses to his plan on profiting off the faked kidnapping of his daughter, who then attempted to steal the money for herself. Though Lianne is unaware and blind-sided by the revelation, she faces the possibility of being charged as an accessory to the crime. She has a final, private conversation with Keith and allows Veronica to walk her out. Veronica, tired of fighting, finally forgives her mother and embraces her in a hug.
In Mr. Kiss and Tell, it is revealed that Lianne was awarded custody of Aurora after the end of Aurora's trial, and was apparently found innocent of the accessory charge. Veronica notes how she is quietly helping Lianne fund Hunter's life, helping to make ends meet.
- Veronica Mars
Bohrer filmed scenes for 1x03 (Meet John Smith), but they were deleted.