I have a few details in my head about it but it may be of two separate stories.

The setting is historical Asia.

A noble family is told they have to marry (or something similar) their daughter off to the royal family but the eldest daughter is beloved (and called the most beautiful woman in the country iirc) so they make their younger, mostly neglected daughter take her place.

Another scene (which I think might be of a different manga but still has a sister as a main character) has the MC being forced to go to attend an engagement selection thing and she encounters the man shes started to develop feelings for. Not knowing hes the man for the engagement selection she states she has no intention of being selected.

There may be reincarnation or isekai elements? I am worried there might be more than just one or two. I also remember a scene where the MC goes to a bathhouse and the ML ends up collapsing in her room and she only knows it because of outside knowledge (I'm POSITIVE if this is involved its reincarnation. I think she was a wife in her previous life but got executed for a "failed" assassination she was framed for)

Sorry for all the weird cluster of scenes. I dont even recall if they were good. I was just reminded of them recently