@stilgar
I'd even go as far as to say that she has already come to terms with her feelings! And at this point she knows exactly what she is doing, because of her fear of being rejected. This still doesn't help her to be liked by readers and it hurts Tarou in the end.
So I still stand by my opinion that she is being annoying and now even say being very manipulative of Tarou. Immature hormonal imbalances carry no weight with the kind of wise/smart decisions she has made with the situations thrown at her and Tarou earlier in the series.
What if the older sister can see first love zombies too? And she's just keeping everything to herself? Can she see Eve and her other little brothers zombie? Supernatural abilities may run in the family!
@Kachakali
Unlikely.
So far the ability seems to appear in males only, with Ibisuki being the only exception but she got it from Tarou.
Also she seemed to forget the younger brother's attraction to Ebino. Something that would've been hard to forget if she could see it.
@ebgeek then again it was reveal that some of Tarou relatives can also see FLZ.
So it could be in this family DNA or their blood line cursed with this ability.