Biography (Original Timeline) Edit
Lucy first appears after Arthur Weasley's funeral, and converses with James in the Burrow. Several months later, she, at James' request, researched information on the legend of the Gatekeeper, and sent him several news articles.
She later appears during George and Angelica's wedding, and travels alongside James and much of her family to attend school in America while her father and Harry Potter aid in the investigation of WULF, much to her frustration as she would be unable to attend Hogwarts until the subsequent year.
She decides to pledge Vampire House at the suggestion of Patches, and manages to succeed at doing so. However, problems soon arise between her and James when he attempts to ask her to show him, Zane, and Ralph the inside of Erebus House to help them vindicate Petra's name, much to Lucy's frustration and James' unwillingness to explain his true reasons.
Lucy also volunteered at the Medical College during this time, and keep James and everyone else up informed on Petra's condition after her arrest. During the final match of the Clutchcudgel season between the Bigfoots and Werewolves, Lucy stayed with Izzy to keep her company before her obiviation. However, Lucy ultimately decided to help Izzy get to Petra, fighting their way into the college and stunning several American enforcement agents into the process. This would ultimately lead to Petra's awakening and subsequent escape.
When James and his friends ventured into the World Between the Worlds to discover the truth, Lucy ended up being killed by Judith, the Lady of the Lake, when she tried to save Izzy from Petra's counterpart Morgan. Her body was recovered by Ralph, who brought it back into their reality. Harry took possession of it after the petrification of the city, and was visibly shocked and devastated by the sight of his cousin's dead body.
Lucy's family were left shocked by her death, with her parents visibly devastated, which was still seen almost six months later during the Christmas holiday, when James noted that Percy had a empty look on his face that never fully went away. Her funeral took place in the summer, before the Hogwarts school year began in September.
Lucy's death would have a profound effect on the rest of her family. James carried a tremendous amount of guilt, blaming himself for both not stopping her from entering the World Between Worlds in the first place or protecting her from Judith's attack. Her death would haunt him to the point that he would think about it all constantly during the summer leading up to his 4th year, replaying it countless times in his head, seeing all the ways that he could have responded differently. Lucy's death would also make James more cautious and protective of his other family, as seen when he accidentally called his sister, Lily, Lucy during a night outing, and actively prevented her from accompanying him during his quest to uncover the plot of the Morrigan Web.
Rose also felt guilt for Lucy's death for not trying to stop James from entering the World Between the Worlds. However, Lucy's death would also drive Rose to believe in the existence of the Lady of the Lake, and ultimately defeating her and avenging Lucy's death by poisoning the water she traveled in with multiple dream inducers, driving her insane.
Lucy's death would also affect her uncle, Harry Potter. He would be more proactive with James during the plot of the Morrigan Web, stating that he knew that they were no longer children themselves and that they had seen too much. At the same time, however, Harry and the rest of the adult members of the family actively kept James, Rose, and the younger relatives in the dark during this time despite their insistent pleading, insisting that they focus on their studies. Although not directly stated, this may have been due to a desire to keep their children out of harm's way, and avoid meeting the same fate as Lucy.
Lucy would later be seen with Arthur Weasley when James and his father looked into the Mirror of Erised. And although she didn't say anything, James was still brought to tears at seeing her.
Biography (Alternate Timeline) Edit
In the alternate timeline, Lucy's life follows the same as the original timeline until the events on the Gwendymere, when the original James Potter and Petra Morganstern traveled back in time and Petra sacrifices her life, thus creating a new destiny where the Crimson Thread was never taken.
For the most part, Lucy's actions during the alternate Vault of Destinies likely follow her original counterpart's, such as her joining of Vampire House and interactions with James. However, Lucy never died in the World Between Worlds in the new reality. Subsequently, she returned to England with the rest of her family and attended Hogwarts in the fall, being sorted into Hufflepuff House.
It is unknown how much of a role Lucy played during the events of The Morrigan Web in the new reality. However, when James encounters her in the new reality, he gains new memories that have him recall Lucy's "unfailing loyalty, her boundless inner strength, her almost unconscious leadership." Thus, this indicated that she likely played a major role in helping ultimately defeat Grudge/Avior/The Collector and stopping the Morrigan Web.
When James awakens in the new timeline, he encounters Lucy soon after awakening from his fever and is overjoyed at the sight of her, much to her befuddlement. She asks him what happened with his fever, but James instead asks her if she could tell him what’s been going on with her. She subsequently did tell him everything in the following years.
In the epilogue, Lucy is seen at the Hogwarts graduation, and James later mentiones that he did see Lucy romantically for awhile, and she is currently studying for her doctorate in advanced technomancy at Alma Aleron.