Sorry-too late for a POA.
You will need a guardianship/conservatorship proceeding.
The answer given does not imply that an attorney-client relationship has been established and your best course of action is to have legal representation in this matter.
You will need to go through the court to get the power to make medical decisions for your mom. This is called a guardianship (a conservatorship allows you make financial decisions). The guardianship process usually costs about $4,000 to $5,000 for the person filing the petition; you will most likely need an attorney's help. However, the Superior Court probably has a packet that you could fill out on your own. If your mom signed a health care power of attorney earlier, you could use that, but it appears from your question that there is no health care power of attorney. Another option is to get together with all of your siblings (and your father, if he is still alive) and meet with the hospital's ethics advisor. A third option is to see if the Yavapai County Public Fiduciary will help with the process (this option is less likely).
You need legal capacity to provide a Power of Attorney. Since your mother is incapacitated, she cannot sign one over to you. You can go to court to get a guardianship or conservatorship set up to receive the records while she is still alive. Once your mother passes, you may have to open an informal probate to sign the release as the executor of the estate.