My own theory on Rin
Granted that her recent actions could just be relapses. But nothing in this game ever seems that cut and dry in the long-term. What jumps into my mind more are some of her scenes and her interaction with Yasu during the test of courage.
I believe that at least on some level, subconsciously or otherwise, she remembers her past version/resets, or at least the painful parts. Given that more of the girls are "remembering" more at this point with this Sensei, I think its possible for previous resets emotions to bleed-through and add to what each girl is dealing with. Rin has noticed the ticking before, so maybe she's more susceptible to it?
Similarly I'd be curious to know if there's a "timeline" in each reset, and if her worst days match up in each reset. Granted this doesn't seem as easy to prove given we only have a general sense of how much time passes each time.
Thinking along these lines made me consider what Yasu talked to Rin about before the test of courage. Yasu knows things she shouldn't, so on the surface asking "How long have you been hurting?" seems like a pretty clear case of her knowing about Rin's habits. I just now also wonder if she meant it "through" resets as well?
Just my thoughts. Goodhomie4life