Would you have done the same? *SPOILERS*
I was quite puzzled by the ending at first, to go through all that and see some good people die only to protect the village that killed your friends and would of mutilated you...it just left me scratching my head. But the more I thought about it, the more I see why she did it....the tribe probably thought they were working for the bulldozing company so they found what they were doing was protecting themselves....although in a very vile and terrible way...but they were brought up to realize that cannibalism is a way of life, plus Alejandro was quite a manipulator and she knew this obviously.
Again this left me very 50/50. I found Justine's nightmare was her feeling guilty that she left Alejandro there, then I saw the mid credit scene and obviously Alejandro is their new chief or something...so I wonder if there will be a second one.