Everyone who defends the fmcs mom can lick my ass bruh idc if she's grieving that dosent g...

Fr

Nah I hope she beats the shir out of the MC for being too stupid to take the necklace off even once.

In fact, that she really IS her daughter makes it even worse, in a way. I got spoiled about something regarding her behavior later in the novel; if you don't want to know, stop reading here. I'm basically just ranting, based on the events that already unfolded and the events that will unfold in upcoming chapters.
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Basically, they "soon" find out who she is because of that device they were talking about just before. The mother is a complete bitch up until the moment she knows that Ria is, in fact, her daughter. She then proceeds to act as if nothing happened, and the MC also just doesn't give a shit about the nasty treatment she got because the mother didn't know YET that she's her daughter.
It's okay that she doesn't recognize her. She doesn't need to treat her like a daughter for no reason. But there's a reason why parental figures in stories like "Devoted to Diamond" (it's called "My Family is Obsessed with Me" on MGG, I think) or "The Monster Duchess and Contract Princess" are liked - and it is because they act benevolently and loving to a child that wasn't theirs (or at least they thought it wasn't - in Devoted to Diamond, the MC is already a fully accepted child of the family before they realize she is really their child they thought had died).
They should have realized that Ria wasn't treated like a maid at all, which would explain her "unruly" behavior, compared to regular maids. While they don't actually stop her from pretending to be a maid (and that's a whole other issue I have with the characters around the MC), she's halfway treated like a sister to their own children. The mother could have shown some brain and simply acted reserved, instead of going out of her way to be a complete dick to her. You have to take an extra step to literally insult a child regarding their name.
No matter how sad you are, the child vanished many years ago, and you should have gotten used to that state to a certain degree by now. She simply doesn't have the right to act like this, unless she's a bitch. I mean, technically, as a noble, she has the right. Sure. It doesn't make her look good, though. In fact, I can't stand her one bit.
And yes, you are right: if she wasn't her daughter, it would simply mean that she's a complete bitch to a random child who hasn't done anything to her, and she would also never change her act. But the fact that she IS her daughter didn't actually mean she properly apologized for any of that shit. She literally finds out she treated her daughter like shit and barely feels bad about it at all. From what I was told, it takes half a chapter to go from knowing she's definitely her daughter to them being "mother and daughter" and the "feeling bad" is crammed in there as a side note.
She would have deserved her daughter simply not wanting to return to her.

To be honest, I always hate it when characters don't understand the good things they can have, while literally wanting those good things, because the author thinks that planning to go away into a world they don't fucking know with too much money than they could be protecting on their own (or goods they apparently want to sell, but to fucking whom, as nobody would believe some beggar bastard got this from their own attic - nobody will buy OBVIOUSLY stolen goods! Turn on your brain, man; I hate those tropes like nothing else) is somehow smart and resourceful. But in this case? She has indeed secured herself some money; she also could have simply accepted getting fucking sponsored from the get-go. She doesn't NEED a family anymore. She never had one, and now she has something similar (though I still hate the Ellards as well; that's not the same for the MC, apparently). There is simply no reason for her to be THAT desperate about having a mom, when the person she thinks might be her mom is such a bitch. At least make her actually reflect on herself before accepting her at a mother.

That last paragraph was on point. Basically all of these stories is (usually a female) MC getting a bug up her ass about something she has to do that she doesn't and inflexibly sticking to it regardless of the circumstances.
It's an incredibly frustrating meta-trope.

No bc ur jst like me fr

Yk on this topic I think the author tried to make the fmc seem more "special" and "loved" by her mom so much that she would bully a kid that would've "stole" what was originally hers where it's seemed like the fmcs mom is juts THAT devoted to her kid (who's the fmc) but it just backfired, they could've had the mom just a little reluctant or had her heart hurt whenever she sees the fmc bc that could've been her daughter instead of going the full on bully route, now instead of the mom being a character devoted to her kid and ONLY her kid, it looks like she's jst a bitch to random kids