Kaitlyn is a stereotypical teenager with a busy social life and a confident, put-together personality. She spends her time shopping and talking about boys and diets. Kaitlyn serves as a foil to Hazel, or a character whose traits highlight those of another, because she symbolizes the classic teenage experience that Hazel can never have due. Since Hazel's diagnosis, the two have grown apart, largely due to a lack of things in common. Kaitlyn's biggest concern seems to be what her feet look like in open-toed shoes, a trivial issue that utterly pales in comparison to Hazel’s terminal diagnosis and an effective means of illustrating the unbridgeable gap that has formed between the two. While Kaitlyn goes on a small shopping spree, Hazel ultimately purchases a single pair of flip flops just so that she has something to buy, further emphasizing the difference in their priorities.
Kaitlyn has also begun to treat Hazel differently. She walks on eggshells around Hazel and the topic of death. Hazel notes that it no longer feels natural to talk with her, that "attempts to feign normal social interactions" with people like Kaitlyn are just "depressing" because everyone has grown "awkward and self-conscious" around her. When the girls see a pair of high heels at the mall, Kaitlyn says she would die if she had to wear them. She immediately grows awkward, obviously concerned that she brought up death in Hazel's presence, which confirms that Kaitlyn seems unable to separate Hazel from her sickness. Hazel ultimately makes an excuse to leave early. Evidently, the girls no longer fit together. Kaitlyn's character serves as a means of highlighting the ways in which Hazel’s illness has affected her relationships with people she knew before she was diagnosed, and the extent to which she now feels a distinct sense of “otherness” in their presence.