Based on how overall Noriko is as a person in front of us players, and also the fact that Maya admits this is something she never dealt with and did not know for sure in
What Is, I'd say Maya is still mostly conjecturing Noriko's impact on the current Sensei and not because she has solid evidence on Noriko's dirt. I am not even fully sure if Noriko ever met Sensei or even Maya after the cycle started. If they haven't met one time in millions of cycles, what or when does "last time" mean in
Stop Looking For Answers? pre-cycle?
(tbh I believe one of the purposes for having Noriko this character is to prove that Maya can be wrong even when it's about the one only thing she cares)
I think a part of it has something to do with what Maya came to "misunderstand" about the cause of breaking Senseis. His memory of the tutoring past has always been the trigger to kill a Sensei (need verification), so those memories must remain locked at all costs. Thus when someone who also holds the trigger shows up with a higher tendency of spilling the beans, Maya goes panic and basically starts exercising extreme preventive measures, but all based on the "incorrect" conclusion she arrived due to her limited personal experiences: whoever knows Sensei's secret past is dangerous.
(using the word misunderstand and incorrect as loosely as I can because this isn't something revealed to the players, either)
I'd say to really break a Sensei, you have to either
tell Sensei a very specific part of his past that involves Maya, or
have Maya actively tell him literally anything slightly important (in fact I think Noriko ALMOST broke Sensei during
Loxosceles Reclusa, but I think that was because she mentioned Maya during that).
The only piece that I think may relate to Noriko's possible deeds or on a broad aspect why Sensei disappeared the second time is in
Baby Finches.
View attachment 2662335
(most of the time [redacted] takes place when the names Akira/Sekai/Maya are mentioned. But here it can't be Akira or Maya, and Sekai is already dead; filling them with Noriko and old district seems seamless, but this is a very wild guess and close to a baseless accusation tbh)
But if true, her deeds were confirmed "serious", and it backs up my belief that no matter what Noriko may or may not done, it was pre-cycle and not because she once broke a Sensei.