yandere != "I'm gonna kill you or some other people!"
yandere == "I love you so much I'd rather see you dead than belonging to somebody else and if anybody shows interest toward you, they're dead."
So far, that new girl didn't show any romantic interest, obsessive or not, toward yuzumori. If anything, she looks like she hate her guts. And she doesn't even know who's Mimika. Calling her a yandere is, in my opinion, premature.
Might get proved wrong later, sure, but this chapter doesn't really show her as a yandere.