The most notable to many readers despite the unrelenting Grimdark fantasy setting will be when Ciri gives herself up to Vilgefortz at Castle Stygga. He chokes and fondles our heroine like a doll before discussing the horrific experimentation he will subject her to all the while hyping himself up into an astonishingly terrifying A God Am I speech. Since he's been a picture perfect stoic villain in all his other appearances, this sudden turn to prancing maniac proves that he was always completely amoral and bat-shit insane despite the excellent Faux Affably Evil mask he presented to Geralt.
He wiggled his fingers in front of her eyes and suddenly grabbed her face violently. Ciri cried out and tried to escape, but he held her firmly. Her lips trembled. Vilgefortz saw this. "Child of Destiny," he laughed, and from the corners of his mouth dripped foam. "Aen Hen Ichaer, the Elder Blood... is now all mine!"
Vilgefortz's description of the, ahem, insemination procedure and the subsequent vivisection will turn your bowels to water and deserves its own bullet point.
The fact that both he and Bonhart want Yennefer to be Forced to Watch her foster daughter undergo this nightmare as well.
What Ciri went through after she was beaten by Bonhart at their first fight, beginning with being forced to watch as he severed the heads of her gang.
Earlier in The Lady of the Lake, we get the dubious pleasure of Ciri's run-in with the hermit simply known as Gramps. Anyone who's played the first game before reading the saga will find themselves hoping he's not like his similarly-named counterpart; who (claimed) he only cannibalized the dead and dying in the Vizima forest swampland. Well, those of us who wished it were dead wrong. He's far worse.
Even earlier than that, Time of Contempt features a much longer Trauma Conga Line for Ciri that pretty much sets up all the following. Starting with her being separated from Geralt and Yennifer, lost in a desert, starved and dehydrated to the point she has to eat lizard eggs and drink mud, is nearly killed by an insectoid monster that wasn't in any Witcher guidebook, is nearly possessed by Falka, gets captured by misogynistic brutes who beat her, humiliate her, and drag her along to collect a bounty, tie her to a post near another group who are eager to gang-rape her, rescued by a group of highwaymen, end up killing a bystander, and finally ends with her being raped by Mistle. Its telling that Ciri ends up deciding to stay with Mistle and the Rats, because while their relationship with her is toxic and one-sided, she can't bare to be alone anymore after all of that.
Special mention needs to go to the relationship with Mistle, which is full of grooming on Mistle's side. Putting aside the fact Ciri was traumatised after another near-rape from Kayleigh, but Ciri was also about 14-15, and Mistle, though not stated, does infer that she's older than Ciri, so even without the trauma there's a massive imbalance of power. Ciri also, as the rape happens, feels both horror and disgust, but also pleasure and comfort in not being alone, all of which is confusing and distressing as it makes her unable to figure out how to feel about any of this. She latches onto the positive feelings because its the only way she can find comfort at this point, and continues her relationship with Mistle after, but after their "first time", Ciri went to have the medieval equivalent of a Shower of Angst, crying at how she'd never be clean again after being defiled by Mistle.