Stacey Nelkin was adorable in this. *Spoiler*

LOL!

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That's what I'm going with. She seemed like a completely different person once Challis saves her/reunites with her after she is taken. In the first half of the movie, Ellie is pretty talkative. But once she is saved, she doesn't say a single word. The Ellie we got to know from the first half of the movie would said a couple things. Even if she had to whisper. Plus she was lacking facial expressions once Challis saves her. It's like she had just one look on her face the whole time once she is saved. But her face was moving all around in the first half. And then there is that why would Cochran go through all this trouble to get Challis to come to the town his factory is in? Plus why was he specifically targeting Challis? Also, Cochran's androids/robots don't speak much. They are very silent. The only time I recall an android ever speaking in the movie was when the one told Cochran that the camera in the room Challis was tied up in was down. Maybe once more when Cochran and the androids are watching Challis and "Ellie" trying to escape the factory through the surveillance cameras. Ellie just seemed too talkative in the first half to be an android/robot when comparing stuff. So to me, everything points to she was a human for the first half and then was killed off and replaced with a robot/android.