Who is Lena Louise Ironheart from Cold Fire and what is their importance?

Lena Louise Ironheart was Jim's grandmother. She raised him from the age of ten, after his parents were killed. Lena died at the age of fifty three. Jim blocks out her death and remembers nothing besides crying at her graveside. He later realized that her death was linked to a visit to the windmill on one of the nights that Jim left the house. The day of her death marks the first appearance of The Enemy.