Can they changed the parent's doctor if they are unhappy with the doctor? Can you take the parent off of meds if they feel the side effects are bad? Can they chose who attends family meetings and who has the right to health care information? What other authority does the evoked health care proxy have?
This is hard if the parent is not have 100% dementia (a term I hate and think is outdated). How do you respect what is left of the parent's thinking capacity and what is best for the parent ?
Not sure what "100% dementia" looks like in any single person but if you are with this LO every day you will be able to determine if they make sound, irrational or harmful decisions for themselves. If it's either or both of the latter 2, then the MPoA needs to step up.
The process in my state was to take the documentation for active authority and the MPoA paperwork to each and every doctor the LO sees so that they can make a copy of it and have it on file. That's how it worked in both MN and FL where I am MPoA for 2 LOs.
Access the above online and Dave Ramsey (as well as a ton of other sites) have a good explanation of what a MPOA is. It can accomplish exactly what it is written to accomplish so read your own document. Basically you are to follow the wishes and dictates of a competent person who appointed you when they WERE competent, to carry forth their wishes, and mostly at the end of life.
As to what powers you have when end of life issues are not at the fore, that becomes very dicey when you start to tell doctors what medications can or can't be given. That would occur only when your principal was adjudged incompetent by the courts. Otherwise, even in a person with limited understanding, medical care will more or less go as they wish it to go when speaking with their doctors.
The MPOA usually has access to doctors, and to records and tests if required. But most MPOA work is done at end of life, when the person with dementia is no longer competent whatsoever in their own care, when decisions for Hospice and Palliative care come to the fore.
As to the word dementia, I am wondering what word you would think preferrable? We used to call all manner of unique conditions "senility" when I was a young nurse, and we had no idea of various conditions extant such as Lewy's versus TemporalFrontal, versus Alzheimer's (and a multitude of others) etc. I find dementia ever so much better. Wondering what wording you would prefer? Most words are too nebulous. When you use something like "mentally compromised" you get into "in what way?" and other questions. I don't find the word dementia to be in any way derogatory, myself.
Consider discussing your own MPOA with the physician in care of your parent; that person will be more familiar with your own document, the patient, and the laws of your state. I sure wish you the best of luck.
She did have a diagnosis of Alzheimer's dementia by then.
Meaning of dementia in English
dementia
noun
a medical condition that affects especially old people, causing the memory and other mental abilities to gradually become worse, and leading to confused behaviour:
source: Cambridge Dictionary.