for me it's wrong to read it like a juge. She messed up her life, was unhappy, and want to correct that in death.Both of them are fucked up.
Be it Kiku or Mahiru, feels bad for them tbh. But then again Kiku doesn't deserve happiness from someone's pov.
For me it's relatable enough to empathise. i don't need or want a moral justification.
she's a villain sure, but this manga is not about that.