She didn't break shit. Once her daughter hits middle/high school is going to be the same batshit stuff again. As shown at the beginning Shiina is a millimeter away from breaking down and the moment her daughter forgets to give her headpats or enters her rebellious phase she's gonna snap.
The dude's daughter isn't moving forward but backwards, she got a gangsta boyfriend and by her smug face we can conclude she learnt nothing and most likely thinks that being a vengeful, stabby bitch is the way to go since that got her her current fame.
The mom seems okay from what little bits we saw. Kinda sad that it took her daughter going to juvie and her family falling apart to decide to get fit and take care of herself (mentally and physically). She wasn't a good mom and should have got some kind of punishment for that but life is a russian rulete.
The dude continues to be a piece of shit until the very end since apparently he didn't even take responsibility for his mistakes (on both sides) and still wants to feel like he's the victim.
I'm going to disagree regarding Shiina's ending, because this is probably the best end result with her. We learn that ultimately Shiina's mom didn't want kids (Chapter 13) she was casually swept in the moment of passion, Shiina herself was an extension of her desire for a man. Her mom hated her way before she was even a teenager, it was when she was becoming a burden in finding a man. She realized she was becoming exactly like her mother: she wasn't having the baby for her happiness, she was having that baby to try and get Iwashita to fully commit to her. (Chapter 16)
This is also something we learn about Iwashita (in Chapter 15), where his decision to have a child ultimately came with a desire to tie himself to his ex-wife. But then once Kokoa was actually born, he lacked as a father. That was probably the biggest catalyst to the two growing distant, even he hadn't realized it till then.
But then she realizes climging onto some random man, who is as wishy-washy about commitment, is exactly how she'll end up unhappy. Abortion was still an option for her by this point too, she had an alternative path, but then decided to keep the child.
She's not crying because her daughter didn't dote on her, she's crying because she's having a hard time as a single mom (other moms and her coworkers gossiping behind her back. hectic schedule, etc.). If anything this is perhaps the most normal expression of sadness she experienced through the entire course of the manga.
She's already leagues above her own mother. Their house properly contains children's toys, it looks clean and well kept, she manages to find time to make her a bento, they actually do outings together, she's actually reading books on parenting and self-improving, etc. And most importantly; we don't see a single man around her. She isn't tying her value around her body and how men desire it, and she didn't keep the baby out of false expectations that some man would love her for it. She became a mom out of her own volition, and even after years pass by and her daughter is a bit older, that doesn't change.
