Do we know if it's Drycha, or is that just our supposition though?
When we scried them, all the clues point heavily towards it:
you find yourself flinching back from a sense of bottomless wrongs, and you find the alien cadence of recited evils springing to your lips. Bone splinters beneath your fingers and suddenly you are back in the hut, left with nothing but the echoes of festered wrath and the smell of lilac.
"Bottomless wrongs" "alien cadence of recited evils" "festered wrath" and "smell of lilac" are all really poetic descriptions that match Drycha very well.