The Tragedy of The Villainess합법적 악역의 사정

It's an oddly hard to follow novel, not sure if it's intentionally vague or the translation. The beginning especially was very strange and confusing but I figured out what was going on eventually. The basic plot is that the villainess transmigrated a year ago and has been cleaning up her life and trying to befriend everyone or at least clear death flags and even gets engaged to the guy who was going to kill her in the novel for the heroine and they genuinely seem to love each other.

Then the heroine actually shows up and everything goes to hell despite her best efforts and she ends up married to the male lead who is the [standard icy cold tsundere who nobody understands but everyone respects] to save her life due to some weirdness of the world. They go off-script almost immediately after that from the novel and there's no scenes of using prior knowledge at all.

There are demons in the world and both she and the female lead have purification abilities but so far it's mostly just background info. It's mostly the relationship between her and the male lead.