This isn't just respecting a patient's decision. It's enshrined in law, under the Mental Capacity Act (I believe). If you have, say, a chest infection and need antibiotics, provided the infection hasn't caused your judgement to become clouded, you can accept or decline the antibiotics. You cannot demand them. Nor can I pin you down and jab you with them. Similarly, with your relative, we can't enforce treatment, even if she would die as a consequence.
No they weren't, as explained above. The alternative would have been for the doctors to break the law. Which brings us back to assisted suicide - it's still breaking the law.
And how, pray tell, would the vet consult with the animal?