This is so confusing and badly explained... Why, just from remembering a past life, she al...

This is so confusing and badly explained... Why, just from remembering a past life, she already assumes that everything is gonna happen like her past life and even decides that she has to avoid the second Prince? Why would she avoid him like he's guilty of something when she was the one who chose gave up her life for a lil bitch who didn't deserve it? And how could she even come to terms with her reincarnation so fast? There wasn't even time to cope and reflect (￣∇￣")

Also, I will never understand this type of oppressive narrative when the one who has the power and is needing by everyone is forced to follow unreasonable rules. She's the saint, she has the power to save people or not, so why does it feel like she's beneath the nobles? The same goes for most hero Isekais, unless there's multiple heroes, doesn't make sense to oppress them to the lowest point when they could just refuse to fight and save the kingdom... Manipulation and two facedness makes a lot more sense than straight out manipulation.
I do know that in this particular story she died because of direct manipulation, but my problem is with the "duty" to sacrifice her life for the douchebag princess. Why was that a duty in first place? Why is the life of the one who posess the precious holy power who can save millions of lifes worth less than one princess?