Respectfully snipped for space.
The reason so many are assuming that her higher brain is not functioning at all is that the doctors who examined her testified so.
...the results of that examination indicated that Ms McMath had sustained an irreversible cessation of all functions in the entire brain, including her brainstem....
...reports of all these EEGs confirm that Ms McMath has no cerebral activity.
http://media.nbcbayarea.com/documents/CHO+-+Physician+Decls.pdf
Exactly. Her whole brain is dead. Her higher brain and her brain stem. There is nothing getting perfused up there.