@Nicegirl Thing is others shouldn't find out their secrets. Others shouldn't know that blonde rabbit has eating disorder and no one can save black hair except her.
@Megami she could tell the other girl that Minjae is sick in the stomach today and was told to not eat much or else he'll throw up. But he is to nice to decline some invitation like that so he will probably force it down. Making up half lies/half truths is always the best way. Everyone will think its just some stomach problem not a permanent disorder and she can go save her BF.