@Jay "I assume for now that Haegu making Mian an instrument of her own self-loathing was out of guilt for inflicting the same suffering she experienced as child, but it was a selfish choice in the end, regardless of the reason".
At first Haegu was going to kill herself right after killing Mian's father. Then she saw Mian and decided to let that girl kill her instead, because she saw herself in her: that way she would allow the girl to get revenge, just as she was given the right to, and at the same time end her miserable life. I don't understand how Haegu is using Mian as an instrument for her own self-loathing. She could just kill herself anytime according to her initial plan. She regretted what she did because it ultimately made someone experience the same thing she did as a kid, and is willing to get punishment for it in hopes of making that someone feel better, that's all.
"She at least could’ve not killed the man in front of her"
She didn't know Mian was there. Do you really think she would've done that if she knew, given her past?
"She could have placed Mian in state care, failing that. She did not take any of the other kids she rescued, mind you. So if her top priority were actually Mian growing up into a functional, adjusted adult, then the story would never have happened."
Haegu's top priority was Mian having a normal life AND getting revenge. If she had placed Mian in state care, she wouldn't get that chance.