While my sister sleeps / Barbara Delinsky.

Enhanced descriptions from Syndetics:

Following the success of The Secret Between Us, a book the Boston Globe hailed as "one of her best," Barbara Delinsky returns with another moving and deeply satisfying novel, this one about the unique and emotionally complex world of siblings. Molly and Robin Snow are sisters, and like all sisters they share a deep bond that sustains them through good times and bad. Their careers are flourishing--Molly is a horticulturist and Robin is a world-class runner--and they are in the prime of their lives. So when Molly receives the news that Robin has suffered a massive heart attack, she couldn't be more shocked. At the hospital, the Snow family receives a grim prognosis: Robin may never regain consciousness. As Robin's parents and siblings struggle to cope, the complex nature of their relationship is put to the ultimate test. Molly has always lived in Robin's shadow and her feelings for her have run the gamut, from love to resentment and back. The last time they spoke, they argued. But now there is so much more at stake. Molly's parents fold under the devastating circumstances, and her brother retreats into the cool reserve that is shattering his own family. It's up to Molly to make the tough decisions, and she soon makes discoveries that destroy some of her most cherished beliefs about the sister she thought she knew. Once again New York Times bestselling author Barbara Delinsky brings us a masterful family portrait, filled with thought-provoking ideas about the nature of life itself, how emotions affect the decisions we make, and how letting go can be the hardest thing to do and the greatest expression of love all at the same time.