Real trans girl this time just to confuse all of them
that's my prediction too
my first thought was another femboy crossdressing, but it looks like her chest does have a curve to it. so either she's upped her game to using pads, or she has them for real
and this scene feels like a weird play narratively if she's just another cis girl that likes feminine "boys" like Tamako
so with that in mind, with the overall direction, I would imagine this new girl is a tgirl with proper hormone treatment and everything, which is then gonna introduce to Ui and Ryuuko that transitioning is a legit option. cue egg angst