"is that not just yuri?"
no.
"girl yaoi", in my opinion, works within the classic, perhaps overdone, tropes of yaoi (or at least some of them)
so there needs to be some degree of antagonism, basically. it can't be too sweet or wholesome. at least one of them needs to kind of suck a bit, at least for a little while. she can get better but a smidge of toxicity is required at some point.