"Effective October 1, 1990, a patient may authorize the withholding or withdrawal of nutrition or hydration under certain circumstances. Ch. 90-223, Laws of Fla."
Terri had her "accident" in February of 1990, so when she supposedly made her statement that she would not want to live like that, it was still illegal to withhold food and water.
In case you haven't noticed, it is now after 1990.