Note, again, that White Court "demons" are not yet actually proven to be an independent thing. (Harry seeing something he parses as Thomas' demon in BR is a datum that has doubt cast on it by the WoJ about how what one sees in a soulgaze is subjective; it's not that far away from how he sees Molly's friend's addiction as if it were an independent monster, under the Sight, in PHG.)
At one point, JB was asked if Mab could remove the demon-thing from Thomas. As I recall, he said yes, she could rip Thomas' demon right out of him, the problem would be that it leave Thomas in a ghastly state if she did it. That implies a certain separateness, at the least.
Also, pretty much everybody who soulgazes a White Vampire sees the things. Carlos made a reference to it 'that silvery thing' after soulgazing Lara, for ex.
I don't think there's any question that there's
something in there initially separate from the human, though they made become one thing after the first feeding.
Or she could, unlike Harry, be just Lawful enough to figure "a chance to save the entire world, implicitly including my son, from Outsiders" as a greater good than "taking my son away from the White Court" and have acted accordingly.
Yeah, but that's so rare that it's never the way to bet.