Who is Marian Catlin from All the Little Live Things and what is their importance?

Marian Catlin is a young mother who has recently battled breast cancer, and she wants to provide her child with a brother or sister with whom she can spend time. Marian becomes pregnant quickly after her breast cancer treataments, but unfotunately, her cancer returns in the sixth month of her pregnancy. Marian does shortly after delivering her baby, who only lives for a very short time.