
Yeah, I get the difference between the two girls with red hair, I was confused as to what happened with our female lead (black hair) and her sister. I was confused on if her sister (red hair) was the one who went to the palace in the past? And if our female lead decided to take her place on coming to the palace instead. Cause I’m confused on if the female lead’s sister was originally with the emperor, and if the female lead wasn’t involved with them, only part of the ones who happened to get executed along with the sister

It probably makes no difference either way, though, because in those times justice usually declared families of the culprits of certain types of crime as "guilty by association". This being a story by an Asian autor, it probably follows the "Nine familial exterminations" rule for triators even if it's placed in a Westernish setting.
Am I the only one who’s still confused as to what the plot is? Like was her sister (red head) the one who was empress in their past lives and our female lead just a bystander? I need some explanations cause I’m getting all the info mixed up.