Origin
At some point, the Inmate Girl was committed to Arkham Asylum where she would become obsessed with Batman.
Creation
The Inmate Girl was created by writer Cyrus Voris & penciler Chris Bachalo for Batman: Gotham Knights #26 in the second story
Major Story Arcs
Bruce Wayne is Batman!
The girl summons The Dark Entity from her cell within Arkham. The entity promises the girl anything she could ask of him and she asks for the true identity of the Batman. True to his word, the Entity revealed to her that Bruce Wayne is Batman. Overwhelmed with joy, the inmate repeatedly shouts “Bruce Wayne is Batman!” for the Asylum to hear.
Learning of the girl, Batman later disguises himself as a janitor and breaks into Arkham in order to protect his identity. When Batman and another janitor pass the girl’s cell, Batman says the girl claims a different person is Batman every day and her obsession with Batman led to her placing in Arkham.
When Batman leaves the Asylum, the girl spots him and sheds a tear.