Tatiana de Rosney's novel, Sarah's Key, centers around two people. One of them is a young girl named Sarah Starzinski and the other is Named Julia Jarmond. Sarah was ten years old in 1942 when her family was part of a Jewish roundup at the Velodrome d'Hiver in Paris. Part of the story is told from Sarah's perspective; the rest is told by Julia, a journalist who researches Sarah's story sixty years later. These two narrative voices tell Sarah's story.
Your question is about the choices Sarah makes and what motivates those choices. In one sense, there are very few choices Sarah gets to make. She has to wear the yellow star marking her as a Jew; she has to be herded into an indoor stadium with thousands of other Jews; she has to watch her parents get taken away from her; she has to live her life in hiding until the war is over. Despite that, there are four major choices Sarah does make which change the course of her entire life.
The first and most significant choice Sarah makes is to lock her brother into the hidden cupboard when the policemen come to take her family away. Her motivation for this choice is simple: she is trying to protect her brother. Unfortunately, she is unaware of the danger for Jews at this time and makes a bad decision; however, her motivation is pure.
The second choice Sarah makes is to escape from the camp with her friend Rachel. Her motivation here is a bit more complex. Mostly she is driven to go rescue her brother; secondarily, she wants to escape from the camp to preserve her own life. This turns about to be the one choice that saves her life in the short term because she meets the Dufaures and they adopt her as their own. In the long term, this is a choice that eventually causes her death. If she had not escaped and gone to Paris, she would not have known about her brother's tragic death and her unwitting responsibility for it.
A third major choice Sarah makes is to go to America and start over as someone new. It is true she kept her name, but she kept perfect silence about the rest of her life. This choice is driven by her guilt, and for more than twenty years she lives a "normal" life as a wife and a mother.
The final choice she makes is to end her own life. The weight of her guilt becomes too strong, and she can no longer bear the guilt or the secrecy. Her motivation is simply to get rid of her pain.
Every choice Sarah makes is connected to and driven by her first choice--locking her brother into the cupboard. She is consistently motivated by fear (personal, cultural, societal, political) and guilt.
sarah choses to die because of guilt