|I'll just be writing stuff as I find them so some of my comments might be invalidated late on.
In the first paragraph you have, "I saw nothing in the darkness in which I slept." here there is a slight echo of the "IN" and the which is a passive word. You can fix both of these by switch the sentence around a little to something like, "I saw nothing in the darkness that clothed/surrounded/enveloped me." Yes, you lose the sleeping, but you had her waking up so you don't need it.
In the next sentence you have, "I lay still, consciously recognizing the cold on my skin, the hard stone beneath my body, and hearing every minute sound." here you start a litany with the active verb "recognizing" but then break it by adding the "hearing" later on. By adding the second action you interrupt the reader's flow and diminish what had been a lovely sentence. I would suggest changing "hearing" to a descriptive "ING" like whispering ( "and the whispering of every minute sound" I know whispering and minute are a little iterative but I'm just spitballing to show you what I'm thinking.)
In the third paragraph you have, "Gentle lighting surrounded ups, lighting..." here the "lighting" echoes with itself and can be easily replaced with something like "illuminating." You also have the typo "ups" which I believe should be "us."
In the seventh paragraph you have, " deep within which seemed to..." here the two "WHs" stacked on top of one another echo a little.
In the ninth paragraph, you have, "...the stone. The words were so ancient..." here the "THEs" echo slightly. I think it'll read better if you replace the period with a semi-colon and remove the "the" and the "were" so you end up with something like, "...the stone; words so ancient he should not have been able to pronounce them."
In the twentieth paragraph, you have, "...know, I’m afraid,” he replied. “I don’t need you going after him." Here the "he replied" interrupts the flow of reading and the sentence might benefit from its removal. You don't need the dialogue tag because we know who's speaking and the tag itself adds no color to his words. The other thing I found disruptive was the "I'm afraid" it doesn't fit his personality up to now and he's not actually sorry. That type of phrase is basically an apology, but he just bound the MC into his servitude for the rest of his life; he has no reason to tell her anything in the first place.
In paragraph twenty-one you have, "I had decided that his cocky attitude did not require me to be polite." I think this is the wrong way to take you MC, this phrase indicates she's cautious of her new master, that she would be polite if it was appropriate but I think she's a much more compelling and interesting character if she's (for lack of a better word) a dick all the time. It's an unusual but vibrant character trait that suits her very well, so I wouldn't water it down at all.
In the twenty-second paragraph you have, " I shook my head, regarding him steadily with my most unnerving stare." here, everything after the "I shook my head" is telling and thus loses the impact you want. I think an active verb would serve you better like "glowered" or even "just stared at him" might work well also. You don't want to tell the reader what's going on, you want them to intuit it and to feel her anger because it will be much more intimate for them that way.
A general thing I've noticed is that you have a tendency to add dialogue tags where they aren't really needed. Dialogue tags are only necessary when it's uncertain who's speaking or in what tone they're using. You only have two character's thus far and her personality is very clear. Take this phrase for instance, ""I KNOW how it works,” I growled." here the "I growled" is unnecessary because the capitalize "I KNOW" indicates her aggression plus we know her personality and that she found the sound it made unpleasant. So the "I growled" doesn't really add anything to the narrative and slows it down by elucidating something the reader already recognized on their own.
In paragraph thirty-three you have him turning on an electric fire but up above he said he would build her a fire. This isn't a large discrepancy but I think his phrasing would change because to "build a fire" has a very specific meaning that won't really be subverted by colloquial speech. I think he would say more accurate like "I'll turn up the heat once we get there" or something.
In paragraph thirty-four you have, "When the man returned to the room, he was carrying a pair of fleece lined slippers, and a very warm looking housecoat" this phrase is passive when it doesn't have to be. if you replace the "was carrying" with a simple "carried" the phrase transitions from passive to active and reads stronger.
In the next sentence, you have, "Both were too big on me, as the overcoat had been,..." here the "as the overcoat had been" is unnecessary because we know it was too big (you stated as much.)
in the forty-fourth paragraph you have, "I spat the word at him, leaving no doubt about how much I despised it" here you don't need to elucidate on her emotions with the "leaving no doubt..." because you stated her distaste for it up above and then clearly showed it with how she spat the word at him.
In paragraph forty-five you have, "proper names,” he said. “What name..." here the "he said" is unnecessary because we know who's speaking. But, the pause in the dialogue it provides is appropriate because there would be a natural pause there if the dialogue was actually happening. Some this might be just because I don't like the way "said" reads in most situation but I would switch out the dialogue tag for a quick action like him leaning back or something. It's fine if you don't change it though.
That's the conclusion of my line by line; I didn't mention everything I noticed because I didn't want belabor any of my points or be nit-picky. On the whole I found this quite interesting with a lot of promise. You have an intriguing set up with her being his slave and something inhuman, and the bit with her being susceptible to the cold was very pleasing from an organic, world-building standpoint. The two character's you've presented us with a distinctive both from one another and in of themselves. They need a little polishing, though, so that their personalities can really shine forth and interact with one another.
As for the dialogue, it depends on what you're going for. For here, I feel a longer, more proper speech would be appropriate considering her age, though not with a medieval accent. Just stuff along the lines of "I am" instead of "I'm" and a generally more proper and considered speech pattern. (That's just my opinion and should not be taken as any other than such.)
His dialogue felt a little more off. I don't know the vibe you were trying to give him but it was a cross between ivy-league and more colloquial and humorous and they clashed. in this type of situation, a person's speech patterns would reflect their emotions and personality rather than their education. He has a more easy going personality so his speech would mirror that ( more "I'm" and other abbreviations rather than "I am.") It would go beyond just abbreviations, though, he would abbreviate his speech pattern as well. Instead of , "When we arrive, I will build a fire for you" it would be more like, "I'll build you a fire once we get there." Of course, if he is Ivy League then some of his word choices would stray toward the more high-brow but I can't really help you there. In general, though, his speech pattern would be very flowing and easy even with more advanced words.
I hope you find this review useful and wish you the best of luck in all your future endeavors. :D.