Honestly its kind of hard to be mad even if she was real because she had no choice in the matter. Like genuinely she is property that needs to birth a child at that time. There was no other path.
She could have made different choices but basically a child was forced to marry and have a child and become an adult with no help. The maids can't say anything, society needs her to be perfect or else, and her husband loves her but doesn't help.
I feel bad for everyone tbh because they're just part of the cycle. You can even see it in other families, like the girl who went to hide in the school due to bullying and her sins new fiance who has a bad personality and her parent enable her.
I'd agree if we had any indication that he was a good father. He neglected his son too. This is the pot calling the kettle black.
Also, they mentioned her father's death at in an earlier chapter, but I'm getting the vibe that their marriage was mad rushed. And so they didn't get married because of feelings, or at least she didn't. We are getting flashbacks so maybe he fell in love with her, in which case good for him. He got married to someone he loves. But what about her? She may have grew to care for him, but if she had to get married for finacial security then that's sad.
But yeah, she was a shitty mom. Being 17 at the time probably played into that. Now she is trying to stop her 15 year old son from being engaged (to what looks like a bad person). This is part a broken clock is right twice a day, and part lived experience. She should object to this engagement with all that she has, and I don't think she is hypocritical for caring. She got forced to marry to young and hated it to the point of neglecting her son. And is now trying to stop that bad cycle of events by stopping her son from marring too young.
If anything I don't get why the husband is so gung ho about this engagement. His wife was too young to be a good mother. So why would he want his son to marry young too? And this isn't me saying she was too young as a modern reader. In previous chapters all of her other friends weren't even married yet. All of her other friends hadn't yet had children. So it seems that it is okay in their society for a people to be unwed for a few years past coming of age. Why is he rushing things with his son?
If I were in Harden's shoes I would lose respect and love for my spouse of she/he neglect their own child. I know how traumatizing it is to have a parent neglect you.
You never recover from the fact that your parent never loved you, when others kids are showered and pampered with love.
Since this is a manga, I don't't blame Ercella. But if this were a real person, even if the woman had PPTSD, I would despise her.