She's not bland at all, we just don't know anything about her and that's very deliberate since Woo hui literally says in this chapter she wants to know more about her too. She seems to deliberately keep her relationships light and surface level. I assume we'll learn her back story soon, the car crash etc.
I agree, the author is just taking her sweet time to flash out Ji-ho's character.
I think the thing, that's off-putting to many here, is that she thinks acts more like male character, than a female, and they try to bend her into how a female lead usually is, and it just doesn't fit.
But it's neither a mistake, nor bad writing, it's a deliberate decision from the author. First, now we know that she has a background in track and field, and taekwondo, and that she was a sporty tomboy.
And we can see that she basically kept the same attitude, even though she had to quit, and now she's a lot more fragile, than she was back then. We can see that after leaving sports, she just cannot find her place, she doesn't make new friends, and she did not became interested in the girly things, like fashion, but she picked up some bad habits, like smoking.
What this hints at is that, whatever happened, she couldn't really move on, and she didn't manage to find her place again in the world. This not belonging, and not caring is what forms the core of Ji-ho's character. She feels like a male protagonist, because she does not want to belong to the "normal" girls, and she doesn't care about fashion, or even just getting a clean T-shirt, or about the talk behind her back, or about anything that'd be of value for a typical "female" protagonist. She is not a total outcast, she talks with them, and goes drinking with them, but she keeps them at a distance.
The upside of Ji-ho not caring about these things, is that it makes life simpler for her. She is impervious to bad rumors and gossip. The downside is that she really doesn't understand the things she doesn't care about, and lacks a kind of awareness in those topics.
Woo-hui on the other hand IS a very girly girl. Unlike Ji-ho, she does care about all of these things, and it frustrates her that Ji-ho is indifferent about them (Often hitting Ji-ho in the head). And while Ji-ho does care about Woo-hui, she doesn't really understand her at a deeper level because of these issues. That's why she often doesn't know how to treat her, or seems puzzled at what to do.