She is a Primera.
I just understood this too, but yes, she's a Primera. Essentially, they have longer lifespans that most other humans and they have great magical power. However, the price is that whenever she uses magic it take some time off her life. So, if she doesn't use magic she'd just age really slowly (hence why she looks tiny at 7) but when she does she will grow equal to the amount of time that it cost her to cast whatever magic used.
And since the magic she has cast only costs her "days", there hasn't been much growth.
Her hairstyle is so annoying
Annoyed at a children's hairstyle??
No, i feel like the author is trying to make her look aged with that hairstyle which is not suiting her. Her face looks like a kid but her hairstyle is making her look old. It's so contrast that I cant process properly.
So you havent "read" the story
Was there another hairstyle other than the pigtails? I don't remember anything else.
Why is she still so small. Comparing her to the others.. she looks kind of weird- IM SORRY!!