MC has the right approach. Try a different approach every time and eventually she'll find a path that allows her to live a real life. Problem is the suffering along the way and the unseen force that seems to guide things, to a degree, to where she ends terribly. Maybe she has to live her life in a specific way to satisfy whatever is making her loop?
Not sure what can be done about the fiance. Looks like he's fated to be a semi-aware puppet until something changes. Feels bad bro.
This whole thing has to revolve around the sister somehow. I'm thinking there was a loop before chapter 1 where the MC and the fiance were in love and the sister cursed them somehow. Maybe because the sister was too sick and was treated harshly like the MC is now. Sister got killed in a few of those loops though.