Maybe it's just me, but I actually like that she's childish, but can be a little mature at times...I have nieces that act like that too, so I understand. But I think it works for this lakorn because she's a teenager, so Weir wouldn't know what to do with her...and I think that she acts so childish because of not having a father, but knowing his identity...I think a big part of it is because she wants to be daddy's little girl, and get spoiled by her dad, which he does anyways. And the best part is that she's old enough to really understand what's going on.
I think she's a good balance to Weir and Jakjaan's characters, and I know that when her parents start to be even more childish than her, she'll step up and remind them that they are the parents...lol