Some people are calling glasses girl selfish but for me, if the other side put me into that situation, the moment I witness a bunch of bipedal apes butcher a woman, start playing with intestines, then slowly make their way to me is the moment I put the thought of risking my life for someone I don't know into question.
It's realistic; with how much shit she has seen and been through, there's no way her mind wouldn't always try to rationalize her bailing out instead of risking her life for someone that's practically a stranger.
This character is a normal, socially inept girl. Not some OP "I'm so cool I don't give a shit about the situation" MC.