She will end up with the duke but there will be many obstacles, THIS IS A SPOILER GIVEN BY MY KOREAN FRIEND, NOT SURE IF HE IS BULLSHITTING ME OR NOT BUT READ AT YOUR OWN RISK , (I hope its not true T_T )
SHE WILL HAVE HIS CHILD BUT SHE WILL HAVE A MISCARRIGE , she will be mentally scarred but eventually it will get better because the male lead supports he (BUT STILL I HOPE THIS IS NOT TRUE SHE ALREADY SUFFERED ENOUGH IN HER PAST LIFE) oh and the sister will end up falling for the duke ? Or the blonde guy that likes the FMC but anyways due to that she will turn into a bitch and have a not so healthy sister rivalry THATS IT THIS ARE ONLY SAID TO ME BY MY FRIEND SO I DIDNT ACTUALLY SAY THIS IS TRUE