I think the most horrifying thing about Drycha is that she really does think she's right. Coeddil was corrupted by Chaos, canonically even (even if it is in the End Times, egh) if not in the exact same manner as within the context of the quest. But Drycha is literally without Chaotic taint, pretty much. She allied, temporarily, with Be'lakor the First Daemon Prince to kick the elves out of Athel Loren. She is just absolutely certain that if she can get the elves out of her forest, everything will be better and fixed. The elves drew in outside problems, and when they're gone, everything will be great again. She will slaughter anyone in her way to get it done, plotting and planning for centuries and more to get rid of them, with zero moral compunctions - as humanity might regard them - as she is an ancient and highly emotional intelligence of distinctly alien nature to not just humans but elves and dwarfs and everyone else. Everything really is the fault of elves, or at least that is the lens she places matters in. And humans and beastmen too, of course, but primarily the elves. She has ever railed against the pact being sworn between the elves and the forest, and normally doesn't even talk to others, just endlessly rants a mantra filled with the names of all the spirits she considers to have been failed by the elves in some measure or another.
And, ironically, there are parallels to the fleshy beings she hates so much.
There are Sigmarite preachers who burn mutants who were otherwise innocent, Witch Hunters who hang whole villages out of suspicion, Cultists of Ulric who steal supplies and destroy homes from people to 'better prepare them' for the final winter, and so on. Heck, the reason Egrimm van Horstmann, one of the most powerful of Chaos servants in canon turned evil was because some Light Wizards wanted to test the 'purity' of children by torturing them. All for the good of the Empire, yes? Extremists of religion and reason alike, and if there was anything that the dryads worships it is Athel Loren. All for the good of The Forest. Everything she does, is in her mind, for the good of The Forest. Losing Coeddil in the manner she did, however, followed by the realization that the army/war grove she had forged out of the Wildwood's prisoners is going to be ground into nothing, plus Durthu rejecting her entreaties? She's a bit cracked, now. More so than before.