...what i took from this chapter really was "huh, so Tsubaki WAS interested in Tadashi from the start, but was going about it in the immature 'if he doesn't pay attention to me, then he must suffer' way that kids would do".
Until she started to develop those feelings besides just wanting his attention because he wouldn't pay attention to her, and into "i just want to be with him (not necessarily sexually, though it'd be nice...)" - which is the more explicit part we see. After all, as many people here have said, her outspoken intentions at the start, which she admits regretting now, was "I want to get him expelled".
Which also was the first time she had tried it towards someone she plainly didn't like, instead of someone who was at least planning to do something to her, going by her wording here and the previous chapter, and at least supplemented by the school's tapes. Hell, checking everything from the first chapters over, she hasn't thought nor has been shown in the act of trying to get someone, besides Tadashi, expelled simply for annoying her - it is only rumours spoken by other students.
It is hard to think of some comprehensive statement about Tsubaki, with that information in mind. Since it makes sense she would act out like that, with her mix of trauma and privilege feeding into her mental immaturity, but it doesn't make it any less horrific, becoming a perpetrator of the things she herself was traumatized by without really realizing WHAT she was doing. It's all kinds of messed-up.
It makes me wonder if the idea was that by that point, the rumours about her honey-potting people she didn't like was starting to affect her (i mean, it is almost victim-blaming her for getting people expelled, when everything we now know points to it having continuously been people trying to creep on her SINCE CHILDHOOD ALL THE WAY TO THE PRESENT DAY), so she took her unnoticed attraction mixed with that weighting in her mind and just...went about trying to realize her "little crush" with the worst frame of mind possible.