few chapter back MC ask if she know to shoot gun. she said that her father teach her how to used it, how in the hell you didn't know there is a SAFETY on that gun if her father teach her!! *FACEPALM*
MC says to trust hamster (ch 27), instantly ignores the hamster and gets ambushed by a zombie.
MC says to always keep the safety off (ch 22), forgets and have it fail when actually needs to shoot the gun.
She's still a kid and constantly being in danger of death must be pretty tiring (especially mentally), so it's no wonder so forgot to remove the safety under the pressure.