Putting this up as an opener...I see a couple of different options...
1. She's forced to serve as a pleasure slave to a Drow
2. She's raped by another prisoner
3. She's taken away to be a sacrificial slave, which can involve a host of very dark themes.
If you like the overall idea but Dark Elves aren't your thing or you have something else in mind let me know and we can try and work something out.
The interior of the slave pits was a dark and stifling place, what light there was coming from flickering torches that threw dancing shadows over the iron cages filled to overflowing with the press of bare bodies pressed together, human cattle stolen away from their surface lives, their unwashed bodies reeking, their skins glistening with sweat, their fate now in the hands of the Dark Elves who ruled this underground warren. Most would end their days toiling in the mines, under the lash of harsh overseers, their lifespan measured in weeks, months, perhaps years for some, though whether they were the lucky ones or the unlucky ones was a matter of speculation. Others would die an excruciating death, sacrificed to the Goddesses and Gods that the Elves worshipped. And a few, a handful, would serve the foul and perverted pleasures of their Mistresses and Masters as succulent fuck prizes. All those within the cages knew was that those taken away never returned.
Little adorned the pens themselves. A carpet of mouldering straw was spread across the cold stone floor, two buckets, one containing stale drinking water, the other where the human cattle could piss and shit, both taken away once a day, one returned full, the other empty.
This was the World that the slim, lithe dark haired woman named Ja'Heira now found herself in, a world of despair, a world where every waking moment was tormented by thoughts of what would happen to her when her captors came for her, took her from the cage to do with as they desired. She sat now against iron bars, her knees drawn up to her chin, her head bowed, her long dark hair falling forward, trying to avoid catching the eye of any, for the cages held their own dangers for one such as she for some took their own pleasure in the cages, males and female coupling, paying no heed to those around them as they rutted in the straw. Some of those who fucked amidst the filth and squalor did so willingly, but others were simply seized, females flung to their back and their ankles pulled apart by males seeking to take pleasure one more time before they were worked or tortured to death as a slave of the Dark Elves.
Twice she had had to fight off another captive, a male who had thought to plunge his cock into her cunt before he was taken away, twice she had scratched, bit, lashed out as she fought off her attacker. The second time another male had intervened, pulled her would be rapist away, but Ja'Heira had not trusted her rescuer, had scurried away, into the mass of naked bodies. Others had not been so fortunate. They were all naked in the cages of course, male, female, the young, the old, for as far as their captors were concerned they were animals. Rothe they called them, cattle, although she knew that it was also a term for slave.
She had no idea how long she had languished in the cages, for there was no way to reckon the passage of time, no rising or setting of the Sun, not in this subterranean hell. There was nothing but the changing of the buckets to mark time, and she had no idea how frequently they were changed. Ja'Heira despised those buckets, despised squatting above the one that served as a midden in full view of others, trying to block out the foul reek as she added to its contents.
And so she had no idea how long it had been since they had fell upon her village, put it to the sword, burnt the houses, slaughtered those who tried to fight back. They had seized Ja'Heira, with others, bound them, whipped them as they led them away behind their lizard mounts, to this dark underground place.
The slave pits of the Drow.