
My theory is that Jugyeong is still scared of revealing herself to anyone in chance that they would think lesser of her. Even IF they both look the same, new girl could say "oh, u think youre better than me just bc you make yourself prettier?". The girl is super nice, but Jugyeong is pretty scarred from her times of ostracization (sad face). Which is probably why she doesn't tell even her best friend. Its the idea of "they accept me now, but would they accept me once they know my secret..." and if they tell the secret to the whole school. Again, just my theory, bc Jugyeong has bad self esteem, as seen by her thoughts that "there's no way Suho likes me, I look ugly w/o makeup". But maybe I read too many shoujo manga LOL
TLDR: Fear of rejection

nah there's no such thing as reading "too much" lol but agree, now that i think about it guess she is softer than the new girl (i.e the confrontation with that rude customer) so maybe it's harder for her to open up even though they have something in common. guess was asking too much, cause her confiding in the new girl would help her self esteem more then only doing her makeup, but again maybe i'm rushing it and it will all work out - without the need for a full-on confesion.

Honestly, even though the girl seems nice now, I've seen (experienced) too many times that it can change the moment you put your guard down... I wouldn't trust her with that secret, eather. In fact, all the time I was reading it, I hoped she wouldn't be too naive to reveal her true self, at least not yet, and so far she's doing well.

get where ur coming from and yeah there r girls that after helping them the do u bad, been there done that, and so not a fan lol but still don't feel the new girl is bad, that's why wanted the "sharing is caring stick" but get ur side and after all she did help her and is still helping her so all is good.
not come clean and tell her that a few months back she was in the same shoes and knows how she feels... would help more than only doing her makeup... but ok