I would like to be the primary agent. My cousin has agreed to be the secondary agent. What happens if I am not reachable for a short period of time (ie, on a plane)? How does my cousin step in until I am available? I understand I must decline or be incapacitated, but what if I am just unreachable? Is it possible to add a letter to the proxy document outlining the arrangement? My mom has a living will, specifying only comfort care, which I think also simplifies a lot of decisions.
If your mother is no longer capable of making these decisions then it will be somewhat more difficult and you should consult, even if by phone, with an attorney in her area.
Get a copy of the document, and find someone who really understands the details. That will also help you to work out what should happen if you are not available.