Responses

Yeah, she is naive and yes her story does not add up but we are aware that it doesn't add up because we know the friend's personality.
Yes, the mom would've thrown it away in the main bin; that is the actual reality of how a mother would act
But Ajin saw no reason to think too much into her friend's explanation
6
We know she has a shitty friend because we have audience knowledge. Ajin has zero reason to doubt or see any issue with her friends actions.