So, just read through this after seeing that you translate this manga as well and damn it's real good. But I have to wonder, did she accept the snake possessing her because she knew that was the only way to keep herself bound to him forever or to save his life while also keeping them together no matter what? Did she just know no matter what that that slasher was going to target them?
If that's the case that's quite the yandere, going so far as to literally die so at least your spirit/body can always be there even as the snake has control. Probably why the OG girl was looking so pissed in the reflections this chapter, they were apart too long.