She chooses to harass him,a bystander, instead of the people that actually bullied her in her youth?
My guess is that the author needs to find justification for female lead's borderline harassment against the mc (aside wanton cruelty) so author-sensei pulled out this nonsensical 'youth bullying revenge' plot but that only makes everything more convoluted since mc is a beta male and participating in youth bullying will be out of character for him,so author has no choice but to make him a literal bystander.Huh.
This makes me even less sympathetic to the female lead.It makes me think that she is a coward and causes me to lose interest in this 'confrontation'