The only moral way is for her to go naturally with attempts being made to feed and hydrate her by mouth.
Otherwise, it is murder.
The slippery slope of government enforced "right to die" becomes "the unfit are only fit to die." It's only a matter of time.
You, of all people, should realize that only the free exercise of my informed will makes me human. If I lose that to age or injury or infirmity, I should have the right to keep 'modern medicine' from keeping my vacant body 'alive' in a vegetative (non-volitional) state. If you concur that I do, then we must agree that I can have some recourse to enforce of that right if the stronger or the more evil or -- as around here -- the louder, the more intolerant and the more absolutist should wish to deny me that right. This is true, a fortiori because this right comes only to fruition when I am, by definition, most weak and defenseless.
Now, I can hope that my family members, to whom I entrust this sacred duty to assist me in ending my abuse and defenselessness, will keep their heads down and below the radar of the 'physical life at any cost' absolutists so popular here. But is my homegoing to be at the mercy of one disaffected relative wanting a crack at my estate? Can they intimidate the government from enforcing my directives and thereby sentence me, as they did poor Terri, to years of forced feeding and diapers? And the government upon which I relied to enforce the sanctity of my contracts is then to stand idly by while they pump me daily with nutritional slurry and change my diapers? And, I am supposed to do exactly what to escape the clutches of the absolutists -- will myself to stop breathing?
No, my long and vigorous life in support of this government earns me their cooperation in protecting my escape to Heaven, bypassing the slurry and the diapers. I have earned and deserve enforcement of my advance directive. After all, we know that we are not like "... the rest who have no hope." Our 'life' is not to be found in some vacant, slobbering, incontinent, twisted body 'cooing one syllable sounds' which only the desperate and the denying would call 'life', but in the vibrant, glowing Life to come with our Lord. Our true home awaits.