From the UDDA (Uniform Declaration of Death Act):
An individual who has sustained either 1) irreversible cessation of circulatory and respiratory functions, or 2) irreversible cessation of all functions of the entire brain, including the brain stem, is dead. A determination of death must be made in accordance with accepted medical standards."
Teri's case seems to be borderline, since her higher brain functions all were dead (cerebral cortex included) - the only thing still functioning was the base of her brain which controls bodily functions.

Here's an interesting article that takes both points into consideration: http://ww2.wcnc.com/Global/story.asp?S=3121668