Why the sarcasm? She could be Jenny Sells, couldn't she?
Mostly sarcastic about my false tone of certainty. I think it's super unlikely that Jenny Sells is Kumori, but there's just nothing that really supports the idea. Plus she'd have to be old enough in Grave Peril to accompany Cowl to the party, and I had her pegged at, like, ten during Storm Front.
My overall point in the post was that there is so little information about Kumori that the suspect pool isn't usefully small. We basically know she's tall enough to hold a knife to Dresden's throat (as has been pointed out in most threads), that she's idealistic, particularly about magic, that she knows necromancy (at least enough necromancy to temporarily halt death), and that Dresden knows her. That pretty much eliminates Murphy and hardly anyone else. And, like I said, with necromancy being a relatively unknown quantity (what are the functional limits? Could someone be resurrected from the dead, like Kemmler evidently was? Does Cowl know how to do that?) you might not even be able to write off dead characters.
She's really only present for... what, three speaking scenes, total? "Priscilla" in White Night tricked Dresden for longer than that. How do we know it's even a woman? Maybe the reveal is that Kumori is actually... Ebenezar (*cue musical sting*). Not really, of course; it's just that there are so many precedents for unorthodox disguises, like "Priscilla," not to mention illusion magic, faerie glamour, and even platform shoes that make even physical descriptions fallible.
Brainwashing is a thing—see Elaine. Cowl definitely has the juice to pull it off if Justin did. Can you even tell if her idealism is her own? Does she even remember being Kumori, or is her memory being tampered with like Dresden's was in Small Favor? Might very well be a persona that Cowl just activates whenever he needs a flunky, and there's precedent for the kind of mental domination it'd require. Hell, the Darkhallow might have had enough of a magical backlash that Cowl's mental hold on her was broken, which is why she's not seen with him next time he shows up.
Then people like to toss around time travel, and that just completely obliterates any names you might otherwise eliminate—Margaret the Elder, Maggie Dresden, and so on. One of the reasons I hope time travel isn't really confirmed to be a thing that Dresden can do is because then every hanging thread can be answered with it. Who's Cowl? Harry from the future. Who tried to run Harry off the road in Proven Guilty? Harry from the future. Who fixed Little Chicago? Mouse from the future, after finishing college and becoming the first Pupper President (he'd have my vote).
Not to say Mr. Butcher couldn't do it well, because I think he can, but it would play merry hell with pretty much any hanging plots and is a pretty messy way of making everything neat, if that makes any sense.
For me, the frustrating thing is that Harry doesn't seem to care about Cowl and Kumori's identities nearly as much as we do, so we're never going to know until he runs into them and literally unmasks them.
Anyway, the overall point is just that there is not nearly enough information for me to make a real guess, so pretty much everything I say about Kumori is sarcastic—which isn't intended to diminish anyone else's ideas or take away anyone's fun, I promise.