I've mentioned a few times by now that my interpretation of Yukari Yakumo is that she's secretly still a human being, so I guess I could probably stand to actually explain it.
So, this is what the Perfect Memento says about Yukari. The actual canonicity of PMiSS is in flux, I think, it was written in a much earlier era of Touhou when ZUN seems to have had a somewhat different vision of things and not all of it has remained consistent even accounting for that it's deliberately inaccurate, but we'll ignore that for now. Making strong assertions about something as clay-like as canon in Touhou is a losing game, in any case.
Akyuu's claims seem to check out. We can, actually, independently verify that Yukari does not collect fear from Gensokyo - most characters seem to be only vaguely aware of her at best (and the more they know her, generally, the less they respect her) and in Forbidden Scrollery we see that the human villagers are so unaware of her that showing up to a ghost story circle and telling a story about very specific identifying features like her gaps only provokes confusion.
On the other hand we haven't been shown any of her activities in the outside world. We cannot verify that she collects fear there. More importantly, Akyuu can't verify that.
A youkai that never attacks humans is by definition not a youkai. The youkai Yukari does not attack humans in Gensokyo. Therefore Yukari is attacking humans somewhere else.
That's the logic here. Akyuu is faced with two facts that don't fit together, so she invents something that resolves them. But she doesn't know anything. This may not be true, and if it is, it's of no relation to Akyuu's claims.
We could formulate this problem differently, if we were inclined to.
A youkai that never attacks humans is by definition not a youkai. Yukari, who claims to be a youkai, does not attack humans. Therefore Yukari is not a youkai.
That she's human specifically is a particular leap of mine because I like the idea. I like what it says about Yukari as a character and about her particular situation. And we know from Sakuya that humans can be immortal without ceasing to be human. But looked at with as close to dispassion as I can manage, the evidence is probably weighted more in the direction of her being the Hakurei God. Depending on how you interpret certain dialogue in Missing Power, she comes within an inch of outright saying it, even.
There's also that Yukari and Reimu have long been shown to have different expressions of the same essential powers over borders, boundaries, and other distinctions. This would tend to support the idea that Yukari is the Hakurei God, but I like to fit it into the "Yukari is human" hypothesis by just saying that she's the shrine maiden of the Outside World's Hakurei Shrine. After all, we know it exists, and based on what Rinnosuke saw of it - assuming Yukari's telling him the straightforward truth about what he saw - clearly someone's taking care of it.
Regardless, by presenting one interpretation, Perfect Memento also provides the evidence and uncertainties that make up that interpetation. In doing so, it opens up entirely contradictory interpretations. The wonderful thing about the arts is that the same material can be taken so many different directions. We are obliged to admit that [1 + 1 = 2], but nothing compels us to submit to [youkai ^ !fear -> elsewhere] when [youkai ^ !fear] could mean any number of other things.
I choose to believe that Azmaya draws Yukari with massive hair vents in SPELL simply because it takes place around the turn of the millennium, and that was just fashionable with anime women at the time. (Manga women? You know what I mean.)