But they did. Greer could not of pulled her feeding tube without the help of the 1999 Florida law that decreed that a feeding tube is life support - just like a respirator. Of course, the compassionate Greer took it just a tiny bit further and included any oral nourishment as well. That is why you have seen all types of people being arrested for trying to give her a drink of water.
They legislated, but they did not legislate enough. They left too many ambiguities, and even though it's been years since this happened, they have not fixed them.
That's the law that should have been named "Terri's Law." It was passed in order to kill her. You are quite right, as the law stood before this change, they had no authority to pull her tube. Felos knew it and is thought to have lobbied for the change. When the feeding tube was redefined to be "life-prolonging" "medical care," then Terri (under the right of privacy) could refuse it. Suicide is illegal, assisted suicide is illegal, but you have the right to decline further medical treatment.
Terri left no advance directive and DID NOT choose to refuse medical treatment. Ah, but the law can overcome petty technicalities of this sort. It declared her incompetent to make the decision and then made the decision for her, while maintaining the legal fiction that she made the decision even though she had nothing to do with it and they themselves made the decision, understand? The law is a wondrous thing.
For the sane observer, this poses another huge problem. The law was changed nine years after Terri's injury. It was not possible for her to give informed consent to the supposedly "medical" decision they used to kill her.
Taking an innocent person's life is unconstitutional under both Florida and federal law. The court made itself complicit in murder.