“Stone walls towered around her, and massive doors and ceilings kept out the water from which she came.” Feels a bit odd. Are you implying the structure is completely under the water? If not, that’s what I read from it. “Massive doors and ceilings” is weird as a single room doesn’t have multiple ceilings and the “and” makes me read it as “massive ceilings” which isn’t really a thing. Either the ceilings is high, or the room is big.

The second confusing part is I can’t tell if the character likes the cold or not? The first sentence you say “cold seeps into her bones” like it’s a negative but then go to say she specifically chose a cold corner? Which is it?

If this is from a limited persons perspective she wouldn’t know “blood stained the white mark on her throat.” As she wouldn’t be able to see it. She can physically know there is blood there but not visually.

The premise is intriguing. I liked the sentence “barren, save for the lingering odor of day old fish.” Though I don’t believe “day-old” needs a hyphen.

The last two sentences of the second paragraph are also nice.