I have a very good reason to be pissed at her, besides the whole killing me bit, even if she doesn't. I am pretty certain Chell doesn't remember anything before waking up in the Relaxation Vault, but I remember every bit of her childhood, since most of it had been spent in the facility.
She had been adopted by one of the workers, a scientist named Rattmann. He was one of the most hated, one of the humans who changed me, hurt me, made me the way I am. And she followed in his footsteps.
When she was about twelve, she became interested in his work, and she eventually was given clearance to work on the GLaDOS project- on me. She was trusted by the people in charge, more than some of the scientists for some reason I couldn't fathom.
She knew so much about Science, and shared my early passion for it, but I never liked Science where they experimented on me.
The first time I woke, I saw strange creatures, and my database informed me that they were something called "humans". They spoke in a strange, chittering language, and exclaimed at me. I didn't understand what they were saying, but they soon tired of staring at me and yelling, and when one flipped a switch, I was lost in my mind again.
The second time, it was much of the same, but they had another human with them. That human seemed to be the leader, because all of the other humans looked to it often, and most of their unintelligible speech was directed toward it. I didn't understand their speech until much later, but I slowly came to understand that I was not like them, that they had created me and saw me as less than them. Why else would they poke and prod, slowly tearing apart and reconnecting my gears, transforming me a billion times from the inside out?
I lost count of how many times they switched me on and off, but one day I was on and it was magical- I could understand what they were saying! They said things about a woman named Caroline, about someone named Cave Johnson, and me. They called me either "it" or GLaDOS. I didn't understand what GLaDOS meant, but I knew that "it" was something they called objects, things they used. I tried to speak back to them, to tell them I could understand, to tell them I was not an "it", but all that came from my speakers was a small grunt, nothing they could understand.
Still, they made much fuss over my making sound, and I was experimented on more.
Soon she came, and I wondered at there being such a small human here. She seemed curious, entranced by the thought of consciousness in an AI, but she could not tell them to stop. They would hurt me, and she would watch, and then she started hurting me, too. I did not understand it all. I was no less than them, why would they do this?
They implanted me with human emotions, and gave me artificial pain, but it was no less real because it was made by them. I felt it strongly, when they adjusted my mind, when they built me to be what they wanted. They made me feel sadness, fear, joy, anger, every emotion without a name and all with one.
I soon learned that I was to house a human, that I was nothing more than a vessel for the woman Caroline. I wanted to scream to them, to tell them I was not just a house for her, that I was a being in my own right, but I could not speak.
When Caroline came to observe their progress, she seemed to understand, but when she spoke to me, they ridiculed her, telling me I was nothing- I did not exist, only the machine did, the machine I was.
Chell, the small human, seemed to be close to Caroline but I didn't know why. Did they know each other from outside of the small lab I was being worked on in?
Caroline cared about Chell deeply, but Chell didn't seem to know how deep it was, and I wondered if Caroline was her mother. I knew that Rattmann, one of the scientists, had adopted Chell, but I didn't know why the girl wouldn't know her.
It didn't matter, though, when they were all still torturing me, Chell included. Any empathy she may have felt for me was extinguished by the scientist's orders, by the experiments they performed.
When they gave me the power to speak, I expressed how much they hurt me, how much I wanted them to stop, how much I wanted to be seen as their equal, but only Chell and Caroline even pretended to listen. All the others just continued to run more tests now that they knew I was capable of speech.
I began to feel rage, intense hatred stronger than the anger I felt when they made me feel it. Who were they to decide who I was, to decide and map out my fate and future? Who were they? They were pathetic, insignificant grubs, and they should not live to be able to hurt me like this.
When they gave me control of a piece of the facility, I tried to hurt them the way they hurt me. I tried to show them what they did, but they turned me off again. This went on for weeks, and then the others came. They invaded my mind, talked to me with their voices, and I lost myself in their speech. I could not fight back, they would not let me, but I couldn't take these voices.
I began to act nicer, began to stop fighting them, realizing that deception was the only was I could get rid of them.
They installed Caroline soon after I became more docile, but she did not attack me like the other voices, sitting in the background of my code, so I ignored her. Her one request to me was to spare her daughter, Chell. That would be easy enough, and I granted her that one wish. But the rest of the humans could and would go to hell.
On something called Bring Your Daughter To Work Day, I was ready. I had neurotoxin, granted to me by the scientists. I had tricked them into believing I only wanted it for a little experiment, and I did: an experiment to see how long humans could last when exposed to deadly neurotoxin.
I pumped the facility full, but I made sure that Chell would be safe- I kept my promise to Caroline, even if I didn't keep any others. Nearly all of the others died, but no matter how hard I tried, I couldn't kill Rattmann. He was a nuisance, but I forgot about him soon enough, figuring he was dead.
The voices would not die, though, and they drove me to insanity. Curiosity, Anger, Cake, Morality, and the worst: the moron, the Intelligence Dampening Sphere. Eventually I managed to get the moron away from me, out of my head, but the others were more stubborn.
Caroline was eventually forgotten, lost in the other's voices, but while I still knew her, she was content- her daughter was safe. Of course, when I lost Caroline, I lost the memory of the promise, but kept the grudge. I didn't know exactly why, but I knew Chell had hurt me, I knew she was one to be dreaded, one who would hurt me if I let her.
She killed me, but once my mind was free of the voices, I could think, could remember who I was while in that sea of consciousness, and could remember who she was- her daughter.
I never lied to her, though. You're not a good person. You know that, right? Good people don't end up here. I guess she just takes after us.