How does the author use foreshadowing in Before I Fall?

In Day Three, Sam thinks back on the fact that she has been best friends with Lindsey since the seventh grade. She knows her better than anyone, and loves her deeply. This thought foreshadows the secrets Sam will uncover about her friend in the later chapters of the novel, and based on her reaction to the teachers', the reader can safely assume that this new viewpoint from which she will view Lindsey
will certainly alter her understanding of her best friend.