Please Don't Die

When Katie O'Roark receives an invitation from the One Last Wish Foundation to spend the summer at Jenny House, she eagerly says yes. Katie is ever grateful to the anonymous "JWC," the person who gave her the gift that allowed her to receive a heart transplant. Now Katie is asked to help others who, like herself, are facing medical odds against them.
Being a "Big Sister" to Amanda, an eleven-year-old victim of leukemia; Chelsea, a thirteen-year-old candidate for a heart transplant; and Lacey, a fifeen-year-old diabetic who refuses to face her problems, is a challenge. As the summer progresses, the girls form a bond of friendship as they behave "just like healthy kids."
When a crisis occurs and one of the girls does not get to fulfill her dreams, the friends are devastated. The girls vow to gather each summer, so long as one of them is alive, in honor of their dreams and of a friendship strong enough to endure beyond this life.
From the Paperback edition.