
U know personally I feel she is in a worse possible scenario. Her best option which I think she can do now is pretty dark
Kill her father (or perhaps get him kidnapped n pretend he has died) n making her act like she needs to return to the position of head of her family now then officially breaking off the marriage. She should then lock Shinpei up in a room. Then she should threatening Shinpei up by putting a knife around her own neck that if he doesn't get his shit right she is killing herself that instant which will get Shinpei to act normal. Then ....I don't know somehow make Shinpei pretend as a foreign noble who is offering a marriage proposal to her then in a pretend get married to him then ...I don't know steal lots of money from her house n run away with Shinpei to some far away land n start off fresh . What do u think?

I think, she should should just hug shinpei and shield him from others while begging him or threatening (by saying she'd kill herself) him to stop and then welp I think she should run away with shinpei while the other three who were with shinpei protect them from other. run away as far as they can and settle down and live happily for what so counted day she has
Everyone in the comment section is asking why isn't the FL doing anything. Tell me what should she do?
1) Run away - only to get caught after 10 mins
2)Ask the 2nd ML to release Shinpei - She did and even begged him too that resulted in nothing
3) Should help ML overcome his every problem - From the past 40 chapters she was exactly doing that only which she thought finally worked but in the end he returned back to his Psycho tendencies
4) Should jump in between the fight - only for Shinpei to end up protecting her n seeing her beloved dying
5) Should ask to stop the wedding - Only to end up making enemies of the most powerful family of their country....she is already not able to handle her father, how will she handle the duke
What she is doing currently
Knowing that duke 's family are sympathetic towards her with the eldest son liking her . She was trying to gain their support n suppress her father ( even if she had to marry) in order to atleast protect her loved ones from almost dying again . This way no one has to die . Later with more time given to her , she could have convinced 2nd ML for a divorce which she believed she could. Perhaps because she thinks she could die any moment, her priority should be protecting the ones who care about her rather than her future which she thinks doesn't exist.