
I think my main problem with the FL, is that she doesn't act like an adult in a child's body. She acts exactly like her age or at the very least a formally abused child. I'm just having trouble believing she's reincarnated. I still like the manga but I'm having trouble believing she's 18 with her logic and maturity.

See, all of you have extremely valid points, very sound analyses. The issue is that you're applying this to a manhwa that seems to have forgotten its FL is eighteen at heart, and just wants to use huge ass manga panels to flaunt how cute she is. The manhwa looks nowhere near even attempting to incorporate all these intelligent reasonings by the readers; at its heart, it's a very shallow manhwa that jams down your throats on her cuteness and expects readers to think so the same way everyone in the manhwa does.

I can see why you think that way but what do you mean by eighteen at heart? Like I said before she wasn’t exposed to social situations or mingled with others her own age. She had to mentally raise herself so obviously her mental maturity isn’t that of an eighteen year old. I guess we’ll have to wait and see if her character will develop later.

First of all, I said I liked the story. If I hate it I wouldn't even be reading it. There is nothing wrong with having some critiques about how it is written. That's how authors works and genres improve over time. I'm sorry this comment is not overly praising a manga you seem to really enjoy.
My main problem is that I notice a lot of works throw in reincarnation because it's popular but it's not important to the plot or overall story. Why not just have her be a child abused in an orphanage? If she's 18 make me believe that she's 18, without having to remind me that every other chapter.

Nope. They didn't. Here, once again, we have reader intervention whereby traumatic or PTSDesque reasonings are applied to a manhwa that has no self awareness over this nor will they ever acknowledge it. How do I know this? In the beginning, her reasoning and judgment is sound enough to tell us that there is indeed a young soul inside her, definitely more than 5 yrs old. By each panel, you're gradually realizing that the author is more interested in portraying her as a cute adorable baby girl, complete with flowers. She deals with her supposed 'trauma' while beautiful flowers sprout around her. Every soul in the manhwa thinks she's adorable. She walks like one, talks like one, breathes and cuddles in her blanket like one. I can't enjoy it cos... she's 18 inside.

I will say in in regards to the twins' story vs this one, here the FL died not too long post her abuse. She lived her whole life being abused and in forced isolation, then died and was reincarnated.
In comparison, with the twin story, the twins lived I think ~25 yrs in a different world, then were reincarnated and abused. And I think that's where most people were having an issue. Because even before they were abused, they lived in our world normally up until adulthood, but that that has NO impact on the story. It doesn't affect their decisions, their personality, how they view the world, etc. (This isn't to say that you can't be negatively affected by abuse at any age, just that those years in our world haven't affected anything)
As such, with the twins, you could make a strong case for removing the reincarnation gimmick and just have them be abused, and very mature children. And given that the story gives an actual in universe explanation for kids in their family to be more mature (literally) than their peers, it just makes it more glaring how useless them being reincarnated is to them and the narrative.
Back to this story though, her being reincarnated did have an impact, as it allowed her to understand that she shouldn't go with the guy who picked her up because she now knows that she'll be abused and will die. Simultaneously, the previous life of abuse (particularly the isolation) gives good reason as to why, even after being reincarnated, she isn't going to perfectly handle the world outside.
(Woof! This is long ( ̄∇ ̄") I'm not trying to start up anything btw I just wanted to give my two cents about the twin story, because I also had to drop it (● ̄(エ) ̄●))

Hmm I think you misunderstood me a little. I'm referring to the fact that from an artistic standpoint, the artist is more interested in selling the 'cuteness' in almost everrryyyyyythingggggg our FL does, dedicating huge ass manga panels normally reserved for important scenes, to her fashion show and her ^O^ Little chick expressions. She has almost no character development, yet artist prefers to still shower her with flowers in everything. Yes omigath, I think I got it. It's like watching a munchkin chick run around as cute as possible, artist is telling us omg look, how adorable, yet I can't coz there's as a chicken hen soul inside. You (not referring to you the poster) tell me to sympathize with her yet I can't when you're more interested in portraying her crying face during trauma with flowers and cuteness.

Gosh, I dropped the twins story like a hot potato. I'm like, helloooo you all grew up normally and lived normal lives, so why are you acting out and throwing tantrums like a fucking five year old, where's your mature thought processes you showed in the beginning. Yet again readers there were trying to explain their actions away, and I'm like I have had enough yo.
I kinda miss him as a doggo.