Just before the final boss fight, you can see Amanda in the window of the control room. Once you go into the boss room, if you turn around you can see a 2nd window on the back of the control room. During the boss fight, the tormentor will teleport up there and watch you through the window as you kill adds. So basically, rather than killing Amanda, the tormentor just sits up there and chills with her, sipping Nezcafe and watching us fight. Had the tormentor killed Amanda, it would have made her death more impactful as it would have been our fault for not killing it fast enough. Also, it would have been a much cooler death scene if we saw the tormentor pick her up and drain the life out of her or slash her with its scythe and toss her body in front of us. Then we could have gotten a final scene where we hear her last words before she passes and the base explodes. Additionally, this could have caused some drama between us and Crow since he would have likely blamed us for Amanda's death.