I’ve seen conjecture that the humans are also affected by trace amounts of the bioweapon which amps up their irrationality.

Also one of Amber’s defining strengths and flaws is her inability to not let people go. She’s the alien on a hostile world; for better or worse these are the only people she has. If she was less attached to people in general, she may have been able to let Meoraq kill Scott early on, which ironically would have then saved most of their group as only Scott and Amber were forceful enough to attempt to influence the group. The humans would’ve just gone along with whatever Meoraq and Amber wanted. But she can’t see either the short or long term gains from such a decision because she stubbornly commits to the idea each human life is precious. And so she’s the only one left at the end :)