What happens to Lia in Little Earthquakes?

Little Earthquakes was written by Jennifer Weiner. It is a story about four women named Becky, Kelly, Ayinde, and Lia who meet each other at a yoga class for new mothers. Each of the women have different perspectives on being a mother and raising a child. Becky takes a relaxed approach. Kelly is much more controlling. Ayinde and Lia have moderate perspectives in the center of the extreme approaches of Becky and Kelly.
Lia is a mysterious character in the story. Although she gets along well with the new mothers, she has a secret about her own brief experience of motherhood which the other mothers do not have. So Lia has a unique perspective. She has left her husband after her baby died in the crib. Lia feels an incredible sense of guilt over what happened to her baby son. Becky, Ayinde, and Kelly discover that their friendship helps Lia to cope with her guilt about what happened to her son. Consequently, they also become grateful that they have babies and did not have to endure Lia's experience.