Sex outside of marriage is a sin. No, it’s not a sin to have sex when someone has a knife to your throat. But in Maria’s mind, she simply wasn’t going to commit a sin - the sin of sex outside of marriage- at any cost. No one is obligated to allow a rapist to kill them rather than submit. That was Maria’s choice. As I said in my other post, I think her sainthood is more so rooted in the fact that, along with generally detesting sin, she was looking out for Alessandro’s soul, since it would have been a mortal sin for him to have sex with her. And that concern for him extended even after she was in heaven.