Jahi McMath's been declared brain dead by every physician who has examined her. The one family physician, Dr. Paul Byrne, who is the outlier in some respects, doesn't argue that Jahi isn't brain dead. Rather, he doesn't believe that brain death equals death. He is not a neurologist and is not licensed to practice in California.
Alameda County Superior Court Judge Evelio Grillo decreed Jahi dead under California Health & Safety Code § 7180.
Legal documents filed in this case may be found here.