Y'all, come on, the "scary gyaru/delinquent" here is the most obvious misdirection. She's clearly being portrayed to be a lot scarier than she actually is (cause that's how Tano sees her, as she's scared of everything).
If she was the toxic jealous rival type, she would've already been angry when Tano said she's close to Rurika. But she wasn't.
Hell, she even paid Tano a compliment (calling her cute) and said she was into all the guys that Rurika keeps turning down (sure, she could be bi, but at least we know she's into a bunch of people, not madly in love with Rurika).