She is a former librarian who will only talk about her past if heavily intoxicated.
Lainie and her sister are amongst the original "conspirators" for the circus, invited to help with the circus' inception by Chandresh Christophe Lefevre. Lainie and Tara were invited to help as they have a keen eye for "small details" - from the music to the texture of the entrance curtains. Chandresh also remarks that they are also "brilliant with atmosphere".
After the opening night of the circus, Lainie stops aging. She later hosts a funeral when her sister dies after being hit by a train.
Like her sister, Lainie is described as having wavy chestnut hair and large bright hazel eyes, which make the sisters appear younger than they actually are. However, their age is never revealed, and they never mention which of the sisters is older. It is also suggested that the sisters are Scottish with heavy accents, but it is never verified within the story.