So she won't even kiss him at their own wedding and is probably gonna cold shoulder him for a year just cuz of a novel? If she wasn't gonna properly step into the role of her sister she should've stayed out of it. He would've been better stepping around her, marrying the sister and letting the FMC warn the doctors or whatnot to ensure the death during childbirth doesn't occur. The plot has proven to be changeable.
Furthermore, doesn't she realize that if she doesn't catch his heart he could just fall for her sister instead at some point like the original novel? How daft is she? Does she expect him to live in a loveless marriage - - he is a human being with emotional and physical needs, just because she's cool with this doesn't mean that he won't eventually realize her sister or otherwise was the better option - someone who would reciprocate.
If she can change who he marries then the entire rest of the plot is changeable. But setting up a failing marriage ahead of time on purpose is setting him up for long term misery on purpose and doing him dirty. I honestly hate the FMC.
Also people are mad that another girl might come along when the FMC said herself she doesn't and won't love him. Should he be a monk and live chaste and unloved? If another girl comes along and loves him then too bad for her! "I'm not gonna love you but I want you to stick around me anyways" is unfair. I hope another girl comes along, providing an "out" for both of them. If the genders were reversed and it was her who had to live in a loveless marriage, readers would celebrate an viable romantic alternative coming into the fray.