She appears just once.
Hidemi doesn't frequent Seirin Academy, but her appearence is linked to introduce another side of the personality of Teshigawara Suguru.
She's presented as to be another rich kid which tries to take advantages of everything she can get. Teshigawara was her private tutor and slave (he even obeys her when she asks him to lick her foot).
She even tries to get Onizuka as another slave too, but obviously that won't work.
She was kidnapped by Yazuka who tried raped before Onizuka saved her
Her last name can be spelled in different ways, such as: Ohta, Oda or Ota.