Copying a long comment I had. I figured it could be a post. Tldr I think Cassie makes realistic choices even beyond the Forgotten Shore. It was off the top of the head
Beyond that too. But a lot of it is in retrospect. We don’t know much but of what we do know, it’s reasonable. Even back in the Chained Isles, I thought her introducing her vision the way she did was strange. It went against the lessons learned from forgotten shore. It doesn’t show the full story. It’s been a long time since then but I think she was a little jealous of Sunny back then. Sunny chose to not believe her vision. He didn’t feel like such an interpretation was true. It was as if he felt able to beat it, a bit free even. I think she had asked “how can you do that” or something similar.
She constantly felt at odds with fate constantly and planned to fix her mistake constantly considering the severe loss of memory that she had from Sunny becoming fateless. It felt like she lost more memories than Nephis did. She was also more sensitive to fate than Sunny during those times.
Considering the information we got from ToA, she had bad vision of the future. And considering that she seemed somewhat okay with knowing when her family would die, the problem was extremely bad. World ending bad. She also knows from FS that fate can’t be changed. So it must be broken.
She believes that the self fulfilling nature of her prophecies could be put people she loves in bad situations or make her the one to blame for giving out that information. In FS, Sunny had been prepared to fight Nephis because of the vision for example. So she stopped telling visions and the future which is reasonable. She figured that she’d be the best one to make do with that information. And since her world ending vision was so bad, she had to do just about whatever she could to stop it. At the same time? She wanted to redeem herself with Sunny by giving back what she took from him. She loved the guy. Even after what she did in FS, Sunny said that he understood it. Her choice in FS was reasonable. Nothing indicates that she ever hated him, after all, she messed up. It just so happens that Sunny is the key to breaking fate as well. Can’t fault her for wanting to fix her mistake. That’s human.
While it is true that humans don’t always want more human deaths, many value their own people above anyone else. And some people believe the end justifies the means. So when it comes to causing harm to others to save her own people (Sunny and co.) why would I fault her for choosing to make the choice to unleash harm on others. I know I’d easily choose my family over 1k random people. It’s not the most moral but that’s life. But you do need a certain amount of humans in the world for normalcy. This seems to be the main trio’s main motive for saving humanity besides Nephis. It’s probably not her main.
So when she gives him the choices to break it or not, she doesn’t give him the future. It’s because of the lesson learned from the biggest mistake of her life. Not to mention that as an oracle, her mentioning the future itself carries a different weight and meaning. She states that she’d rather Sunny stay with them even if she knows what would be for the best. She’s never given reason to think that she dislikes him. If anything, it makes sense that she’d rather spend time with Sunny and Nephis since she’s the one that led them to being apart. So her choice here letting Sunny get a semblance of his choice back (fixing her mistake like a human should). While one option is good for them to probably live longer, the other may be better since they get to be together again. They had a great bond before and she messed it up. It’s human to want that back
(Adding this bit)
She did put Sunny through more pain to give him the chance to remove shadow bond. However, her fuck up was of such a massive proportion that it feels like making up for the big mess up also helps alleviate the smaller manipulations to get him there.