Well I was going to give my two cents, but Halmoni happened with the Korean perspective to boot. I have to second the sentiment that there's nothing unrealistic about Seol-a or "off" about the way her character has been developed. You can be socially astute but naive at the same time, as can be the case with Seol-a. To be fair to her character, It's necessary to look at how her its been structured to this point.
Seol-a grew up with three older brothers. Do you really think those brothers weren't overprotective of their baby sister and didn't constantly try to prepare her for how dangerous their gender can be (hence the bat in her apartment)? Seol-a is constantly being wooed by a potential male suitor wherever she goes as well, and she's had a few passionless flings. That being the case, I think it's safe to say she has some experience in how to deal with men, although she is still a little naive and that's what got her in trouble with her violent ex.
But what about other women? Seol-a has been burned by them her entire life and she has never ever had a close female friend that wasn't just trying to exploit her or waiting to stab her in the back. Seol-a is brilliant in handling men, obviously possesses great intellect and knows how to carry herself in social outings, but she has zero experience in having genuine relationships with other females, platonic; romantic or otherwise.
Given what we know about her past, I think her interactions with No-rae are very believable. It's a two pronged situation here. Not only is No-rae providing Seol-a with her first real experience in female companionship, but No-rae is also Seol-a's first love (she's admittedly never fallen in love to this point and we all know she's head over heels for No-rae); that is a lot for her to navigate on her own and she has nobody to confide in...other than No-rae. The only other female she bragged to No-rae about in chapter ten or eleven only made Seol-a paranoid, depressed and jealous over No-rae..which is further evidence of how female companionship in general is uncharted territory.
I think she, like No-rae, has been very well written. No-rae is the only female to really penetrate past "Seol-a the Idol" and uncover "Seola, the person." And it doesn't hurt that Seol-a thinks she's the cutest thing ever and obsesses over her lips while trying to blame it on the booze.
Oops, I guess I still gave my two cents. Oh well. Good discussion.