In 28 Days Later, Selena is a badass survivor of the Rage Virus. Her husband gets infected and she ends up having to kill him. Her parents and brother also died at her hands once they became infected. When you have to murder your entire family just to (1) protect yourself, and (2) allow them to have peace, it hardens you.
Selena gets her hands on a machete and teams up with others. She is determined to survive and adopts an attitude of self-preservation. Later, Selena does change her mind on her kill-or-be-killed mental state. But honestly, in that situation, we can’t blame her for putting herself first. And it pays off. Even though she forms alliances with others in order to survive, Selena is one of the last ones standing when the movie ends.
