Secure Poa Status Without Pursuing Guardianship?

Throwaway account - Location: Kansas

I became my mother’s financial and medical POA about a year ago. I knew she suffered from an undiagnosed dementia, but I now know just how severe her symptoms are—paranoia, confusion, delusions, poor judgment, memory loss, speech difficulties, occasional hallucinations, etc. She acknowledges some memory loss, but otherwise is in denial about her condition, so will not consent to any testing.

The POA is revocable which she knows and threatens to use regularly. She will declare certain financial actions should take place that are either impossible, nonsensical, or not necessary because she simply doesn’t understand “It doesn’t work that way.” If I don’t comply to her satisfaction, she gets angry/suspicious and threatens to revoke my POA. My intentions are sincere, but my fear is how vulnerable her dementia leaves her to bad actors if I’m not her POA. She had a couple of close calls before my involvement.

Are there options to make my POA status for her irrevocable, or at least more secure, short of obtaining conservatorship/guardianship? What I consider credible sources are giving conflicting information. A couple say that a letter from her primary care doctor stating she’s not capable of making responsible legal or financial decisions on her own would suffice. And that filing this letter with the attorney who drew up the POA documents would legally prevent her from revoking my POA. Is this true and if not, what other options, if any, do I have to make my POA status more secure and protect my mother in the process?