I get that you have to leave your intelligence at the door and, given the flashback, apparently the dude was super psychotic, but what in the hell would drive a rational thinking human to even let it cross their mind that, oh let me yank out all my teeth so my guy like's me more. This was before the world was twisted from the sounds of things too.
Given that people like this exist in real life, both the abuser and abused (both willing and unwilling), I don't think you have to "leave your intelligence at the door". Especially if we're talking about people in the narrative that apparently are so extreme they are entwined with the creation of this twisted world. Rather than thinking that's so far-fetched, it's more correct to say somewhere in the world, if there's someone this effed up, and that's the person who would be involved in all this.
I think the hint might just be that she's a different breed of vampire.
Some vampires are afraid and can be defeated by Christianity.
While in some other folklores vampires will die if you remove their teeth, this was seen a lot in Europe when people that were suspected of being vampires were dug up out of their graves. Then their teeth were removed from their skull, lastly they would place a large rock in-between their jaw so they couldn't bite anyone.
Thanks
Rigonda for the transition
There's a shit ton of folklore regarding vampires across the East and West, so you may be right, even if it's not this specific reason. Lynn is spoiled for choice here. I recall an example of capricious revenants being afraid of a human who lacked teeth, because they prized their own teeth as a source of strength. This ironically led them to believe a toothless human who could still yet survive possessed powers more unnatural then themselves, as they could not conceive of other beings being able to go without teeth.
Not that it's what the Empress believes, I imagine, but her phobia is being implied to have informed the type of creature she turns into it seems. I don't remember if that was the case with other witches, maybe it was mentioned before.