That's not in the book?
Kind of. In Asher's novel, this same crash happens; it just happens to a lesser-known character. "I never knew the guy in that car," Hannah says in the book. "He was a senior. And when I saw his picture in the newspaper, I didn't recognize him. Just one of the many faces at school I never got to know."
Though Book Hannah feels partly responsible for the senior's death -- after escaping a nightmarish house party, Hannah and a questionably sober cheerleader drive into a stop sign, knocking it over and setting the stage for the crash -- it hits TV Hannah way harder.
Via flashback, we see TV Hannah try to confess her involvement in Jeff's death to Clay. He erupts and shuts her down, upset that she tries to make his friend's death about her. Adding the toxic guilt to the dozen other mishaps that have already rocked her life, Hannah seriously considers suicide for the first time, saying her situation "was starting to be more than I could live with."