Independence feels like the only thing Rin would allow herself to say at this time. Like Shoto said, it's been years that he and Rin have had a genuine conversation and that's exactly why I can't go for Guilt. It's too real of a look into Rin's heart and I don't feel that she is at the point where she would bare herself like that. I mean she can only just admit it to herself, never mind to the brother that she focusing a lot of her resentment on. There's too much distance to connect like that as siblings while at the same time the baggage from that distance can't let her talk to him like an objective stranger.