Wow, so they had a close relationship in the past or what's going on? owo
@itsHanabi agree, I think she has faced these kinds of things many times before, that she's trying to "ignore" or belittle the matter in order to feel less scared; after all, the police can't do much until something bigger or more harmful happens but yeah, it's not a good idea to stay till. Anyway, the most that she can do is to get a bodyguard or increasing the security in the building or changing home, maybe that's why she's also trying to chill.
While I agree with @AiriAi 's thoughts why she acts dismissive about a stalker, it can also be argued that her ignorance of what a stalker can actually do helps to explain her behavior. She hasn't experienced something worth being careful for just yet. I do hope at least someone knocks some sense into her.
from the glimpse of flashback, why i think that shes sort of someone that introduce beomi into the entertainment, sort of? or theyre pre-debut friends. thats why theyre close.