Legal Point: Is there a prescribed form of Living Will in Arizona?

No.  There is a sample form available, but it is not a prescribed form.  It is perfectly fine to sign a Living Will using a different form or even no form at all. 
 
There are, however, specific rules for how a Living Will must be signed and witnessed.  A valid Living Will must be signed in the presence of at least one witness or a notary public.  The Health Care Agent is not an authorized witness, nor is anyone involved with providing health care to the signer.