I'm not the angry one, it's my mom. I living within walking distance of my parents. I take both parents to their doctor appointment. My Mom becomes angry at me even when I haven't been there. She has my Dad, who has lung cancer, cancels her appointments. I don't know how to handle her angry outbursts.
Tough to arrange this if she's uncooperative and can tell someone who the president is and the day of the week.
If she acts out, becomes aggressive, you can call 911 and say that you feel she is a danger to herself and others. You get her remanded for a psychiatric hold and go from there.
A consultation with a good eldercare attorney could also be a good move. S/he might have some other ideas based on your state
Also, even without POA, you can share information about her behavior her doctor.