Nam On-jo.
Yes, she survives the zombie apocalypse, but over the course of two days, she loses her father (Nam So-ju); her best friend (Yoon I-sak); and her love interest (Lee Cheong-san). Admittedly, Cheong-san is just "missing and presumed dead" rather than "officially confirmed dead", but she doesn't know that.
Must have been a very difficult life for her, after all that
. If season 2 ever comes around, I hope it'll be kinder to her.