While it's not on point, Federal law guarantees a death row convict the right of Federal appeal, even though the underlying case is tried according to state law.
Civil procedure is also largely a creation of Congress, adapted by the various states, Louisiana excepted, of course.
Anyway, thanks for the small concession that the question of whether or not the federal judges followed the law is "arguable at best." Whether or not the Federal courts followed the law is not a slam dunk, either "yes" or "no."
Florida screwed this one up. The answer isn't a federal law, hastily written in a couple of days.
It's foolish to count on Congress to get anything right ;-) But it may be that federal oversight is appropriate, in some cases of withholding food and water with the objective of shortening life. Especially where an error below results in NOT following the patient's wishes and killing them AGAINST their wishes. That's the intent of federal oversight in capital cases, to provide a safeguard just in case the state court blew it. The stakes are the same, life and death. It's a minor check on state power and on an individual's right to self-determination, without outright denial of either.
Yet I don't think we know enough medically to really know what Terri's quality of life was. Was she there or not? Nobody did any tests on her this century.
A living will or a medical power of attorney will keep most of these cases from ever becoming controversial. It's not a matter of choosing either PULL THE PLUG or KEEP ME ALIVE NO MATTER WHAT. A thoughtful decision can be made at any point in between.
The forms aren't complicated, and as much as this pains me to say it, you don't have to pay an attorney to fill one out assuming you have reasonable comprehension skills.