Lily was born at some point after her father's future self gave a lecture to his younger self after noticing how he was ignoring Clarissa on her birthday while they were in Washington DC. Younger Martin took his older self advice to heart and conceived Lily as a way of showing his commitment to Clarissa, not realizing they did not have a child in the original timeline.
In Kindergarten, she ended up getting in a fight with her teacher for wanting to sing the periodic table instead of the alphabet. Her father was called in, but was amused by this.
When Lily was in seventh grade, she and her father stayed up all night building her science project, with Martin giving her coffee to stay awake, much to the annoyance of her mother.
Helping her father with the Dominators
After seeing visions of her, Martin Stein and Caitlin Snow visited Lily at their home. She expressed her love for him, before the two rushed away at the behest of Martin. Not long after, Caitlin invited Lily to S.T.A.R. Labs to assist with her knowledge in nanotechnology. Despite attempting to work on a solution to the Dominators, Lily went to leave, to being unnerved by Stein's apparent neglect. Catching her on the way out, he apologized, admitting that his life had become complicated. Sparked by this, they realized that the reaction of their technology required greater complexity to work. Fixing this issue, they used the devices to cripple the Dominators.
After they parted, more events from Lily's childhood began to come to her father in the form of memory flashes. He told Jackson that each one of them was a gift.
Learning the truth
When the Legends couldn't decipher the mystery of the medallion, Stein went to Lily thinking she might be able to find out more. She met her father and Jax at Jitters where he knew he would find her. Jax was surprised to actually meet Lily and even more surprised that she was who Stein had in mind to help them. Lily brought out a portable ionic scanner which Stein was astonished to see in a portable version and Lily told him that she designed it herself. She was able to activate the medallion and Stein quickly put it away and decided to bring her back to the Waverider. She was astonished to see the ship and the Legends were astonished to meet her. She and Ray were able to link the medallion up with Gideon and he took her to celebrate with champagne. As they ate, Rory accidentally revealed that she was a time aberration.
She angrily confronted her father and asked if it was true. Stein told her it was true and she felt horrified. Lily realized that this was the reason that her father had been distant during the Dominator attack. She then became angry as she was sure that her father felt she was a mistake. Later, after talking with Jax, Stein went to Lily and told her that he was sorry for not telling the truth. She said that it wasn't his fault that she was a mistake but her father said that he made many mistakes in his life but she wasn't one of them. He told her that time travel doesn't often give them what they want but it does tend to give people what they need and he needed Lily in his life in ways he couldn't have imagined. They shared a hug and Lily kissed her father goodbye before she returned to Central City.
Lily has been shown to be a very cheerful, warm, and friendly young woman with a rabid interest in science, a trait shared with her father. Lily appears to use science not only as her passion in life, but also serves as the catalyst for her relationships with her father, both professional and familial.
DC's Legends of Tomorrow
- "Outlaw Country" (vision)
- "The Chicago Way" (vision as a baby)
- "The Legion of Doom"
- "Turncoat" (mentioned)
- "Camelot/3000" (mentioned)