No one here is a good person, everyone is looking out for their self interest, but no one is evil for trying to survive.
What would happen if she fought earlier? The monster would still kill them all without a daily sacrifice, she would have to sacrifice him and continue the practice herself, or the rest of them would fight back against and sacrifice her instead. All she did was ensure she'd have more time to prepare for when she would have to fight.
My comment is like over 1 years old. Why do you even bother replying? I have not read this and a lot of other manga since then, because of life and stuff. Pretty much forgotten everything already.
So....thanks for pointing out whatever I didn't understand a year ago......? Whatever that was......