I'm not sure exactly who Sarah is without more information from the story. But she is likely a person who has a weight problem and is the focus of the '600 pound life' story.
I'm a person who loves reading novels and have no practical experience or knowledge to evaluate literary works. Sarah's Key is a fictional novel. I can't comment on it because I don't have any relevant information.
The key in Sarah's story is significant as it symbolizes her connection to her past and her family. It's a tangible link to the home she was torn from during the tragic events.
In Sarah's story, her physical limitations due to her weight were major challenges. Simple things like getting out of bed or walking a short distance would be arduous tasks. Emotionally, she might have faced self - esteem issues and perhaps isolation from others. Socially, she may have found it hard to engage in normal activities with friends or family. And on the path to weight loss, she had to deal with the pain and discomfort of starting to exercise when her body was not used to it, along with the mental battle of sticking to a diet.
Sarah was significant as she was Abraham's wife. She was part of God's plan to create a great nation. Even though she was barren for a long time, her eventual pregnancy and the birth of Isaac were important steps in fulfilling God's covenant with Abraham.