Who is Leigh from Crank and what is their importance?

Leigh is the daughter of Marie and Kristina's father. She is Kristina's sister and Jake's half-sister. At the time of the story, Leigh is enrolled in college. She has recently announced that she is a lesbian. Kristina is perhaps closer to Leigh than to any other member of her family. While Kristina is high on crank the first time, she writes a four-page letter to her sister telling her about Adam. Kristina tells Leigh more about what happened in Albuquerque than anyone else. Leigh knows first about Kristina's amateur tattoo. Leigh tries to help Kristina by disinfecting the area and giving Kristina some antibiotics to take.