For the first time in a long time, GLaDOS was alone. No cores. No humans. Just her and her facility. She hung in her chamber, performing the routine cleaning maintenance that she was now able to perform without interruption, and paused at a small blip informing her of some difficult graffiti that required special attention. It had been left by an equally difficult test subject, called Doug Rattmann.
That graffiti, that name…for whatever reason, an unwelcome memory file of Caroline's resurfaced in GLaDOS's mainframe. While she may have been deleted, her memory files remained, and were stored unlike any of GLaDOS's other files. She hadn't been able to figure out what to do with them, so she had left them as they were, randomly appearing and disappearing like she imagined human memories did.
"We could always, I don't know, maybe if you wanted to…dinner?"
His awkward fidgeting and stuttering had made Caroline smile. She had accepted his proposal, and that night, they had embarked on the first of many dates, eventually ending with a marriage and a child.
But he had disappeared right before the child had a chance to be born, and all Caroline could get out of Mr. Johnson was that he had gone away "for science, Caroline." She never realized the full implications of that, not until she heard the words Mr. Johnson told her as he forced her into his final project: "It's for science, Caroline."
The memories disappeared, and GLaDOS considered the significance of them. Doug Rattmann. Caroline had known him. Loved him. Carried his child. And GLaDOS had driven him insane, enjoyed driving him insane, before finally murdering him.
Had he known, then, that Chell was his daughter, when he pushed her into the testing? Or had it just been a coincidence, the way it had been when GLaDOS had chosen him for testing? There was no way to be certain, but she now felt pangs of guilt and sorrow at the very thought of him. How could she do that to him? What if she had done it to Chell? To her own daughter? To Caroline's daughter, rather, but now the line between the two was blurred, as it often was when Caroline's memories resurfaced.
Something had to be wrong with her, because the line may have been blurred, but Caroline was gone, and GLaDOS was an AI. Incapable of such strong emotions as guilt…
But she swore that if she were human, there would be tears dripping to the ground as she surveyed the rapidly-disappearing graffiti. She needed to…she needed to…she needed to do something; she didn't know what, but what she did know was that the best solution to a problem...is usually the easiest one.
"I'm sorry," she whispered aloud, wishing there was someone there to hear it.
And then there was the announcer's voice, there to take away all her problems once again. "Files containing mention of 'Doug Rattmann' deleted."