Catherine is almost insane with grief over the death of her fiancé in the war. She meets Frederic, and it’s love at first sight.
Booker says the hero is "in some way incomplete" in this stage, and in need of "unusual gratification." Though she is dedicated to her nursing work, it shows her a ton of pain and death. Catherine is lonely, she wants to love, and she wants to meet someone to help stop the pain of her work and the pain of her lost love. Since her attraction to Frederic is instant, he’s the perfect "focus" for her excess "energies."
When Catherine shows up at the hospital in Milan, Frederic returns her love.
You have to be a bit cynical to work this into Booker, where, at this stage, the tragic hero does something bad to get what she wants, and then seems to be "getting away with it." Catherine is at that particular hospital so she can be with Frederic, and she does actually wish there were more patients so that she won’t be sent away. She gets her wish and more patients come, but Catherine’s wishes didn’t cause any of the wounds in World War I. To the contrary, she never neglects her patients and foregoes sleep to be with both the patients and Frederic. All she’s "getting away" with is a little bit of happiness in a very difficult situation.
Catherine and Frederic are expecting a baby, and Frederic is sent back to the front.
Catherine and Frederic are both happy about her pregnancy, but they are also afraid to bring a baby into a war-torn world. But when Frederic’s leave is cancelled because he offends Miss Van Campen, the lovers are ripped apart. Catherine differs from Booker’s tragic hero in that she performs no "dark acts" to keep Frederic with her. Booker also talks about a "shadow figure" showing up to threaten the hero. Since we know she dies giving birth, we suppose her pregnancy could be considered a "shadow figure."
Catherine in labor.
Catherine is doing OK until she hurts so badly that the anesthesia is no longer effective. It’s safe to say that "forces of opposition" are threatening to defeat her.
Destruction or Death Wish Stage
Catherine dies shortly after giving birth to the baby, who also dies or is dead when he’s born.
A Booker tragic hero dies as a result of her own acts, when the consequences of those acts blow up in her face. Unless loving is a crime, Catherine commits no devious acts which bring on her death.