458.326 Florida Statute: Intractable Pain; Authorized Treatment. -- (4) Nothing in this section shall be construed to condone, authorize, or approve mercy killing or euthanasia, and no treatment authorized by this section may be used for such purpose.
782.08 Florida Statute: Assisting Self-Murder. -- Every person deliberately assisting another in the commission of self-murder shall be guilty of manslaughter, a felony of the second degree, punishable as provided in s.775.082, s. 775.083 or s.775.084.
Florida's prohibitions against assisted suicide protects not only the terminally ill, but also the disabled, the elderly, the chronically ill, the severely handicapped.
Withholding food and water by mouth is a deliberate act to end life and is prohibited in the Florida statutes! "Helping" Terri kill herself is assisted suicide and is also prohibited in the Florida statutes.
Patients have the right to refuse medical treatment, and it is not considered assisted suicide, else the law permitting refusal is meaningless - you're not going to find any court in any state that accepts arguments based on the notion that a particular law is inherently meaningless and without effect. In this case, that refusal came via her legal guardian. If you don't like that outcome, and I sense you don't, then perhaps the laws on guardianship should be changed in Florida.