Dr. Elsie Hannaway is the protagonist and narrator of Love, Theoretically. A recent PhD graduate and theoretical physicist, she works as an adjunct professor as well as a fake girlfriend for hire through the app Faux. Since being diagnosed with Type 1 diabetes as a child, Elsie has felt like a burden to those around her and is highly insecure about herself. She has developed a system in which she can analyze what people want from her and acts like the person they want her to be, always putting the wants of others above her own. Her chronic people-pleasing is draining to her personally, and it also begins to affect her career once she applies for a tenure-track position at MIT. While Elsie believes she alters her personality to change others, throughout the book, Jack makes her question whether what she is doing is merely an act of code-switching or a more malicious lie about who she really is.

Elsie faces many external struggles due to her position in academia. As an adjunct, she cannot make ends meet to attend to her medical bills and is so overworked that she has no time to do the one thing she really wants to do: complete her manuscript.