What, to face the reality that the child considers love to be an unnecessary and frivolous burden, has felt that way since birth, and she is a killer who kills entire families without hesitation? Sure she’s doing it now as a sanctioned assassin of the nation, but she’d do it for cash just as easily.
No, to make her face the fact that no matter how scared she is or how she couldn't understand her own child, in the end she is still her child. Her own blood and someone that she should have been beside of instead of an outsider she pick up randomly.
Whether she took the mantle of a mother for her again or deciding that Serena is too much for her is another story entirely, but at least that would and should give both of them a closure, not this half-baked relationship where she still want to be her mother but couldn't make herself actually do it.
I went back to chapter 1, and it was mostly Serena, after being loved for 6 years, just going “how much more of this do I have to endure? Just have to act like a normal child. Dammit, the dog survived; I was trying to kill it. I have to avoid my parents if I want to get stronger in peace.”
So she wasn’t slowly opening up to loved she spent 6 years enduring it like it was a job she had to do, and another 6 years actively avoiding it when she could in order to do what she actually wanted.
... What hurt you so badly that you see the world like this...
I genuinely curious how did you ends up reading (or maybe not) the body language like that. Well, if that is how you see it i can't exactly say you are wrong since we don't have any narrative like in the novel to know for sure (manga tend to deviate a little from the novel afterall)
I was talking about page 14-15 specifically, the scene where after she tries to comfort her mom to not be seen suspicious, she was shocked and seems to feel awkward when her mother hugged her. She could have been depicted being awkward all the time she was hugged or give up and just wait until the hug is finish, but page 15 shows she relaxed a little with her eyes not as big as the previous page and while her expression didn't change much from page 14, to me it does looks more neutral than the awkward look, showing that she relaxed a little but not so much that she looks like she gave up like on page 16.
To me, it's the look of acceptance, where she still have reservation to it as if worrying at the possible danger existing in the background but accept that there is nothing she could do there. She accept not a hopeless situation where she literally couldn't do anything to fight it, but the little protection she could have by being hugged. She even stop thinking about the dog and the attacker for a moment to even start questioning if her mom would still act like she that if she was the one in danger, would she still think about mercy and kindess if she were the one that is going to be hurt.
She was starting to question about her idea of violence for the sake of survival, whether it was something she absolutely need or just something to be used when it truly necessary. That fact alone shows that she was starting to move from her pastlife. IF she were to keep being showered with kindess like that, while she won't be those perfect innocent heroine, she would definitely won't be like her current self. Someone who made herself as the outsider in the house while the actual outsider is acting like the real daughter. She cares only about her own survial and her obligation as the daughter of the house. She doesn't even care about any shit Rosemary is doing that would and could destroy the house like she had no close ties with it.
P.S.
This is also what many mother in our world had to face. A child could be born with neurological disorder that made them doesn't feel fear, so they couldn't learn moral like normal children. They would take risk and can't associate negative stimuli like being stabbed, getting hit, or sudden loud noise with fear that usually stop someone from actually do something, like our MC even if hers is a learned trait and not a born one. Yet they could still be taught about the good and kindness of the world. If they can, why can't Serena also learn love? if 6 years aren't enough, why not 12, 15, 18, or 20 years.