Looks like you can't.
Also noticed you didn't answer my question: What is the ethical reason for forbidding her parents to even try [rehabilitative therapy for Terri]?
To your question:
From an ethical standpoint all the evidence, and the findings of inumerable hearings and court decisions, rehabilitive therapy will not restore Terri's cognitive functions. Attempts at rehabilitive threrapy have indeed been attempted with no change in Terri's condition and further, the Schindler's have failed to provide the necessary evidence that additional therapy will be of any benefit whatsoever. To allow this situation to continue reduces what is left of Terri Schiavo to a legal sideshow. A freak of nature with no right to privacy and a tool of every opportunistic radical group that comes along.
Regards, Lion