Re: Keepers United
Since it seems likely that the witch left the area via teleport or something similar, Nightbreeze isn't going to be able to pick up the scent of where she went, but he has no problem finding the scent of the trail that brought her here.
It does seem likely that the witch went back to wherever she came from, which was somewhere to the east.
Sky's Whispering Lore spell only helps her focus on her knowledge of nature, and it probably wouldn't have been necessary for her to detect the same 'trail of darkness' that heads off to the south... essentially in the direction of the Ents that are in trouble. However, the spell does let her realize that the invisible hut isn't natural (invisibility notwithstanding). In fact, it has such an incongruous aspect that she's pretty sure it's actually some sort of magical item... a cross between the Tiny Hut spell and a portable hole.
It does not seem to have been made from dark magic, though.
The book's title was Torshon's Alkhemaria. The 'potion' that the witch had been brewing had been titled Torshon's Pyroclastic Cloud... some advanced form of the Incendiary Cloud spell. That she was brewing an entire cauldron of it does not bode well, particularly for a forest. The good news was that she hadn't finished it. If she had, it could have laid waste to the entire forest, burning all the trees and plants, killing all life, and making it a desolate place suitable only for orcs and their kind.
It is possible that this was the threat to the Ents, but probably not. It does seem like there might be a connection, though. The threat to the Ents was more dire, at least Radagast had implied that.