I think that everything actually happen, she is only in another dimension. Still, the prince is really shitty
why do we have to look at it your way ? There are multiple ways to see this, here's mine:
The MC did nothing wrong and he was an asshole garbage in every possible way. Do you think anything would have changed if she accepted to be the empress like she did in her past life? No, nothing would've changed. The future is starting to change because she wanted to do things differently. That makes her a better person but it doesn't change how much of an asshole the prince is. Even if it turns out that he was fed some major misunderstandings in the past life, it doesn't excuse what he did and he is the same person as the prince living right now. He just didn't have the chance to repeat all the horrible things he did because she hasn't become the empress
Once she reincarnated, she knew about the girl who was gonna appear and marry the prince. Once she changed her actions she changed the actions of others. The prince has no memory whatsoever of actions he took. Remember, I'm her past life she doted on the prince and he found it as a nuisance. But this is my point of view, it is your choice if you want to make sense of my point or just ignore.
Oml people!!!! Look at it this way. When she was reborn all the actions that the prince took didn't happen yet. Her fate changed course once she was reborn therefore changing others fate too that is how she was able to make so many friends and the prince slowly having feelings too so stop hating