I don't think anyone is actually argueing whether the Burning Man would be able to corrupt any human in Malifaux but a) how it could get to Misaki and b) whether it makes sense from a narrative standpoint.
Concerning a) I suppose it's perfectly viable to assume that something just happens to her out of the blue, like unknowingly walking past one of its portals or powerful minions on her mornig jog to grab coffee and some cinnamon rolls. But some foreshadowing would have been way more elegant. Maybe a corrupted Torakage could have placed an artifact in her quarters. But that should have happened in a previous book.
But b) is more important, I think. What narrative purpose does Misaki's corruption serve and what does it mean for the rest of the faction? Misaki's lieutenants are mostly extremely powerful and intelligent beings. Maybe the Burning Man's influence could sneak past Mei Feng, but what about Shenlong, who is the vessel for a tyrant himself, Yan Lo, who is millenia old and familiar with all kinds of supernatural beings, or the Hungering Darkness who might not be a Tyrant yet but on its way to become one. Were all of them simply occupied while Misaki grew imcreasingly more erratic and ... fractured?