Sensory depravation and "death edging".
Just the fact that in the scene where you get to decide to go through with flirting you ask her if it's going to be a repeat of the alley scene and she says that it's not. Then actually it's just that and more.
I can understand if that freaks folks out tbh, certainly is NOT my cup of tea. I always heard Tessa was an outlier of a character to say the least in terms of who she appeals to. The sensory deprivation is one thing (Like I'm into blindfolds and shit so...) but yeah I'm skimming the github and the "death edging" as you mentioned I'm definitely seeing now. However the thing is the alleyway scene was clearly her giving you an idea of what you're dealing with, "A taste" as it will, like she said.
I'm not blaming you at all for being affected by her hard niche kink btw, a knife to the throat threatening you in sexual stuff or a gun on your back as foreplay is only for those not for the faint of heart. It's just the alley scene if you read it again was actually the big sign post that showed what you were getting into with her. And Tessa doesn't seem like the sorta girl to be joking around as I skimmed her writing (Which you probably would've gotten a feel for with talking to her).
If you didn't stop there and kept going further after seeing that scene, I actually dunno what I can say to help you there. x.x;