i dont get why she's mad i can understand if she was annoyed but idk

i think it’s bc she’s being sketchy by trying to impersonate the female lead

If someone was copying my way of behavior and being arrogant while doing so ESPECIALLY in front of me I'd be pissed too. Not even going into if it was used to hook up with someone...

Exactly and i think it’s also because 7th brother is meant to be engaged to her sister so she is worried that this girl is his mistress and will be mean to her sister