And I am surprised why the girl has two personalities...white hair... ghost girl taking control!
Looks like Ouma offered out her body as a timeshare to a lonely ghost girl. That explains a lot about her situation
Which chapter did that first come up, again? I don't remember how that started at all.
When it started? Well, this is the first that gave any indication that this precisely was what was going on. But let's see...
https://dynasty-scans.com/chapters/sorry_but_im_not_into_yuri_ch24#10 Character introduction chapter, shows she can see ghosts.
https://dynasty-scans.com/chapters/sorry_but_im_not_into_yuri_ch30#20 and https://dynasty-scans.com/chapters/sorry_but_im_not_into_yuri_ch33#17 show her with different hair and eyes, hinting at possession. Which pays off:
https://dynasty-scans.com/chapters/sorry_but_im_not_into_yuri_ch49#27 Where she literally snaps back to normal at the stroke of midnight, as if there was some kind of supernatural arrangement. Moreover, she did not know what she was doing, so it would appear control and consciousness are transferred entirely rather than having her in the proverbial passenger seat.
https://dynasty-scans.com/chapters/sorry_but_im_not_into_yuri_ch49#31 Likewise shows that it has been days since she has seen Toudou herself, despite being in the same class.
Current chapter (56) showed what looked like Ouma, much younger and with her normal dark hair, comforting a white haired girl leaning against a shrine. If indeed she was a ghost as it seems to indicate, then they seem to have come to some sort of arrangement. One in which Ouma gave a whole hell of a lot that she really didn't have to, presumably to help make up for a life cut tragically short.