Even decades in the future, when people's legal awareness would be far stronger, turning in one's own parents and brother would still be controversial. This was even more true in the current era.
To deal with people like Miao Fenghua and Su Dan, appeals to sentiment and custom were useless. The law was the most effective tool. But taking legal action was incredibly difficult, and she couldn't be the one to do it herself.
If she did it herself, it would harm her almost as much as them, and she'd be condemned by everyone. It just wasn't worth it.
She had to maintain her position as the victim, occupy the moral high ground, and avoid the accusation of being unfilial. She needed others to help push things forward until Miao Fenghua and Su Dan's actions were successfully classified as a crime.
Yes, they were Su Li's mother and brother. But what they had done was a crime. Their sins were monstrous, and if they weren't punished, the consequences would be unimaginable!
