Imasara desu ga, Osananajimi o Suki ni Natte Shimaimashita - Ch. 42 - The Uprising of the Nosey Girls

[peortega1]

I doubt Hikari is that perceptive. She strikes me more as an intuitive kind of person rather than someone who can read people's minds.

I don´t say she realized everything in a moment. But her subconscience started to join pieces, this is the moment where she starts to realize Yuu didn´t lie her and in part this is the reason why she defends him and starts to understand how she failed him in the truth moment, not just as love interest, as childhood friend too.
Hikari is starting to realize Yuu talked with Yami about his grief and inferiority complexes about her, she is starting to realize Ayami was the person who Yuu tried to got over her... and failed because Yami dumped him. And this is the reason why Yami changed visibily when she learned Hikari was the childhood friend of Yuu she always hated.
Her instinct definitely is very good to detect when somebody hated her even before meeting...
This is the point she starts to realize why she failed in the moment she didn´t enter in the classroom when Yami slapped Yuu. Why she failed when she stayed in the door as a fool paralyzed by the shock to see "Aya-chan" having a couple fight with "Taa-kun". To have friends like her who let you die in the truth moment...

 

[peortega1]

This "you never would have look Yuu if wouldn´t was for me" is the point where Hikari starts to realize Yuu really said something about her to Yami...

 

[story645]

There is nothing in the text that suggests that she is convincing herself about it being not that deep.

I think it's the words she's saying to Hikari, which are text. And I think it's the whole structure of 41, where Aya isn't ever responding to Hikari's asks even though the pretence of 41 is that Aya is seeking Hikari's forgiveness.