I feel like Haruka's giving those vibes as sort of a red herring.
Or well, not really a red herring, but like, she's said how she's messed up previous friendships by getting overly attached.
Us readers are like, yeah, cuz girl you're super gay and you crushed on your straight friends, you're not some horrible person who gets overly attached, you're just a normal teenager who happens to like girls.
But Haruka feels like she is, and so every time she gets more intimate with Kanae it's sort of got the tone of like, oh shit, she's gone too far this time, it's gonna screw everything up. Except that Kanae is also super into her right back, so they keep progressing their relationship, with them both obviously realizing that something more is going on by now than just being friends.
tl;dr: I think Haruka gives off those little yandere vibes because that's how she feels about herself, but she's actually just a kid with a crush who likes her back.