Ok so spoilers about Rosie:
She was affected by a curse of the dragon(Ambroxia) that resulted in her regaining her memories of the first timeline. MC fearing the outcome, imprinted a somewhat similar imprinting that of those the Homunculus have, to her sister. When she woke up from the curse she was afraid of dying(afraid of ML too) and then told MC that she will support her towards her(MC) being the empress. MC at this time was still reluctant but at the end she was able to prove that she had changed and does not have any plan to kill MC in this life. During the curse, MC feared that Sylvestian(Rosie's Personal Knight) might get implicated because of the condition Rosie was suffering from so she had to take Sylvestian as one of her knights and forcibly take Rosie's imprint and re-imprint Sylvestian to protect him. Rosie also got engaged to one of MC's people(the one’s she recruited). And apparently one of our FL’s child will like Rosie and say that Rosie’s her favorite aunt

I wanna see rosie suffer a horrible death.