Beat the game on normal or hard difficulty to unlock Inhuman Mode.
Last Dino Battle
At the start of the last Dino battle, you should have ten Tek arrows. Use them to shoot the T-Rex in the head while looking for the shotgun to your left. When you get the shotgun, circle around the box where the shotgun was found, and keep shooting her in the head while shooting flares to keep her disoriented. When the T-Rex fall, go to her head, and knife her. If done correctly, you should not have died.
Thanks to Revolution Reader CrypticHill.