Actually, it's better to have a Power of Attorney and a Health Care Power of Attorney. One is financial, one is healthcare. I have them and everything needed went smoothly when I was in a coma five years ago. The hospital knew what to do and the bank knew what to do. Everyone should have them, not just old or even ill people. Even married people. You should also have a living will. And here is the most important thing: TALK to the person so they know what you want. Otherwise, you get what they want.
Hard as it may be, any person, especially an older one, needs to have some one with "Power of Attorney' (POA).Make that a notarized "Power of Attorney'.
Cattlekid, I would call and annoy the hell out of your grandmother until she found it easier to do it than listen to me. The real problem is if two kids disagree and then you have to go to court. Nightmare is right. Whichever offspring she likes best needs to schedule the appt with the attorney and take her there.