Now hold on @qualityhistorygamingwinner you might be onto something.
First of all, how did she exactly hear the Oni masks calling her? No normal person ever would, not even Lloyd heard it at first (possibly because he’s more tapped into his dragon side than Oni but still he should’ve heard something.) and she’s been hearing it for what may as well have been months or years after Garmadon died.
The Oni Masks can be considered relics of spirits since in my AU, they do have the spirits of the Oni Generals. White Oni would have the affinity to collect them and take them back.
She already has a sort of connection with the spirit world, however faint it was.
She’s aloof before she’s friendly. Could’ve been because that the Royal Family hadn’t want to reveal her due to possibilities of anyone eliminating them. (Blue Oni were known for assassinations of royalty, however corrupt royalty were. So they left that affect on them even after centuries passed)
What we can guess if she is part Shiro Oni, is that this Oni stayed in the material plane, ended up becoming attached to someone, not making it back to their original guardian post and making the tribe smaller? They’d eventually have a half Oni cub and it just kept going so on and so forth until Harumi. So the Oni blood is diluted, but it’s enough magic in her to make her hear the Oni Mask and corrupted Garm between the afterlives.
I still feel like the Masks could’ve been alive with the Generals inside. They just needed a body to hold them intact and they could’ve returned through corrupting the wearer. (Don’t mind me using Jackie Chan Adventures logic. It just seems so much cooler in mind.)
So Harumi could’ve very well have became an Oni herself but she wouldn’t be herself entirely. It could be split with the General and the Shiro Oni blood conflicting each other because we just have to remember that Pale Oni had to eliminate and chase away many of their corrupted brethren. They were never thanked for it and instead got hated because of what the others did so they left to the Spirit World, only coming back to deal with any relics involving said spirit world or to pick up any rebellious undead. (I’m looking at you, Morro!)