Is Keiko Numata's backstory the same in the anime as it is in the the novel?
It would be fair to assume that her background is generally the same. All events leading up to and beyond the point you are referring to suggest the same woeful tale. Maybe it was an accident that occurred in one of her insane fits, or maybe they are scars of a previous attempt to contain her. 

One thing is for certain, if you don't want to live anymore, and you want to make a very big mess, bite off your tongue.