Trying to remember a name of a isekai villainess webtoon

webtoon girl possesses a blonde haired princess is diagnosed with an illness and only has a few months to live. Not a kid princess. The princess is much older. Also the sickness she gets diagnosed with is actually her remembering the memories of the person she possessed. The og princess will talk to her from to to time. She'd vomit up blood when remembering.

One male lead is a night who guards her with white hair. another male lead has black hair and is a Duke.

She has a brother who sometime in the webtoon she wears a black veil to his party and basically gives up her line to the succession of the throne