Revealing mistake: When Strahm's phone says "no signal" there is actually a three bar signal. (00:06:35)
Revealing mistake: When Stahm is in the cube trap, there is one shot just before he sees his phone, gun, etc. and you can see a massive gap down the side of the cube where it wasn't shut properly. With the size of the hole, it would be extremely hard to keep water in the cube. (00:09:35)
Revealing mistake: When Strahm removes his jacket at the end of the movie and starts pushing the walls with his hands and uses his legs, when he takes his feet off the wall, the wall moves. Now considering these walls are supposed to be solid steel, this doesn't make sense. The walls are actually wood.
Revealing mistake: When Strahm is being crushed by the "closing walls" at the end, watch closely during the last few seconds. There is a brief shot from above Strahm, looking down as he screams and the camera is spinning. If you watch closely, you can tell the "closing walls" that are crushing him aren't moving during this shot.
Chosen answer: Assuming the woman in the bathtub was able to be moved safely the amount of blood gained from her, while still being helpful, would probably not be enough to save the final two survivors from self harm. Without the heart pumping blood you would only get the blood that was in her arm at the moment. You would have to lift her or raise her so gravity would get other blood moving to get enough. Which the final two possibly could have done, but stress of the situation clouded their judgement.