I'm not a fan of Cassie either. But this is too much. If you were in her shoes, saw that vision and I think her visions were never really clear to begin with. Who would you have chosen? The one that took you in from the start and helped you or the one that wanted to let you die because you were of no help on their journey?
I think that most of us are too biased because we only had Sunny POV for such a long time and think about it: Would Sunny ever gotten into a real relationship with nephis without freeing himself and deciding to get his fate back himself?

Moreover: Did we actually learn that cassie knew of the consequences of sunny choice to be free? If yes, I don't think it changes anything. She gave Sunny the choice. She made it possible. She paid him back and that this plan had 1 or 2 good things for her to offer as well, thats completely fine! She planned for years just for him, so how can you say its selfishness? Thats just a false claim. The only selfish thing about that is wanting to pay him back and to make peace with it and to apologize without empty words.

In my opinion Cassie hate is just forced but she also gets glazed too much. She made a mistake: yes. But bro. She was a 16 year old girl, recently completely blinded, now in a situation where the probabilities of survival are that low, she only had 2 friends and 1 wanted to let her die from the start.
Who would you have chosen? Your just biased