She isn't being portrayed in a better way. People used the fact that she used to be a better mom and that rapr changed her, but look at what harada did. She showed a woman who has no guilt, always hated momo and doesn't even call him her son but "that child". It's just people that can't believe a mother can do such things nor can thry believe that this woman is worse than the man who abused her.
You summed up everything I was thinking. The mother is not being portrayed in a positive light. You have to think a little deeper than that. She is trying to rid her self of guilt to make herself feel better. She doesn't want her past actions to stain her current self. Making amends lets her cleanse away all her previous sins if she is forgiven.
Right, it's unfortunate that a lot of people who are victims of abuse either fantasize about abuse or perpetuate it, but their victim status does not absolve them of their crime. I wonder, too, if her facilitating Momo's abuse was her way of getting back at her abuser--by using him as a substitute. Either way, the woman has issues.
I see that people are saying the last two chapters are trying to portray Momo's mother in a redeeming light, but I don't really interpret it that way. In the latest chapter, especially, her motives are selfish and presented as such. She doesn't bemoan what she did to Momo, she doesn't say that she wants his forgiveness. She met up with him to clear her conscience--to see the kid one more time before she cuts ties with him forever, and the ring is for her to hold on to for nostalgia of the child she cast away. It would be one thing if she was trying to take him with her, or if she got on her hands and knees and apologized or something. But idk...she probably carries guilt but I think it's been buried beneath pride and resentment to protect herself. She's moved on with her life and is living happily. Thinking, 'I am a bad person that did these things to my son,' is probably discordant with how she views herself now, so instead she blames Momo--thinking that he is trash and so these things were bound to happen anyway, regardless of her intervention.
I like this manga because the characters' motivations and thoughts are mostly portrayed through their actions and expressions instead of only relying on internal dialogue. As for Yata's actions, I feel that he's not telling Momo's mom off because he probably thinks resolving things with her will be good for Momo. We've repeatedly seen him want to beat down anyone that misuses Momo in any way, you think all that would change just because this person is a woman and Momo's mom? I give Yata more credit than that, I'm sure he has reasons for pulling back and acting the way he is. (and as for Kuri, I'm pretty sure it's all just research for his book lol)