It's not that Coke is deadly but excessive quantities of anything can be.
From the article:
"she probably suffered from hypokalemia, or low potassium, which he thinks was caused by her excessive consumption of Coke and overall poor nutrition."
"Mornin said that toxic levels of caffeine, a stimulant found in Coke, also may have contributed to her death, according to Fairfax."
"Hodgkinson also said Harris ate little and smoked about 30 cigarettes a day. In the months before her death, he said, Harris experienced blood pressure problems and lacked energy."
"In an interview with The Associated Press, Lisa Te Morenga, a nutritionist at the University of Otago, said excessive consumption of any type of liquid in a cool climate would be likely to play havoc with the body's natural systems and balance.
Karen Thompson, a spokeswoman for Coca-Cola Oceania, said in a statement that its products are safe.
"We concur with the information shared by the coroner's office that the grossly excessive ingestion of any food product, including water, over a short period of time with the inadequate consumption of essential nutrients, and the failure to seek appropriate medical intervention when needed, can be dramatically symptomatic.""