Plot: I like this plot! The only thing I'd complain about is that your description implies that romance would come later in the story, however, already at the beginning there is some, and while I appreciate romance, I think you should put it later. I was expecting it to come with time.

Grammar: No complaints, although since you're not a native English speaker, there are some areas that don't sound natural. I'd hire a native English speaker beta reader.

Style: In chapter one, you switched from 3rd POV in Jennie's section to 1st POV in Minzy's POV. May I ask why? If it's not for a reason, I wouldn't recommend that change. It makes your story seem messy. Not exactly sure if this really relates to grammar, but you seem to switch from the idols calling each other their stage names from their real names. Again, if this isn't intentional, I'd change it, but this time for sake of realisticity. (spelled wrong probably XD ) 

Characters: Not too bad. There's an obvious difference between the rookies and the sunbaes, but I'm not seeing individual character developement as much.

Overall Enjoyment: Personally, I'm not a big fan of yuri, but the story was not a bad one. One thing I'd like to note is that the story isn't quite realistic. Maybe you weren't aming for that, and that's absolutely fine. Maybe it was meant to be fluffy,  (although the cover doesn't denote that) but the romance feels cheesy with no development, and the interactions, eh? I don't have as much of a problem with the latter though, just with the romance. One thing that definitely made me enjoy your story more was its wonderful grammar and correct puntuation. I also think that poll at the end was super cool!

     - I don't know if you were expecting this one or not, but your texts are quite unrealistic. I'm just giving this feedback in case you want to make it more realistic, however, it doesn't really take away from the story as a whole. However, possible pros may be that taking the time to make it more realistic gives readers the sense that you're paying attention to the little details, making it (possibly) more appealing for them. Besides, the text I'm giving is at the very beginning of the story, so you may even want to make it seem that way.

ORIGINAL:

To: Jennie Kim
From: Lee Chaerin

Jennie-ah, go to the dance studio when you have time to see me. (In case you're wondering, Sajangnim gave me your phone number so I could contact you)

TRY: 

[6:23 AM] CHA3R1N: yo jennie!!!

[6:23 AM] CHA3R1N: Sajangnim gave me ur phone number so i could contact u^^

[6:24 AM] CHA3R1N: jennie, wanna come to the dance studio when you got time?

**Perhaps you want it to be more formal-like; in this case, I would keep the same format as the one I have above, however keep what your body of the text message is, which few rephrasings, and maybe put the stuff in the parenthesis in a second text message. Also, just my opinion but, I am not really a fan of the '-ah.' MAybe common in Korean texting, but since it's an English story, meh.

     - It seems a little nit-picky, but this is tips afterall. So in the first chapter, which Jennie eats breakfast in, why is she eating so much? You said 'platters' of food, and when I think platters, I think extremely large plates, filled to the brim, and are meant to eat with a large group of people at a large family meal. Maybe it's word selection problems here, or something? I honestly think that she can't eat that much for breakfast, nor would she be allowed, as thin of a waist she has currently.