She is living alone and has recently named someone other than her niece and nephews as POA. That POA is making us ask when we can visit and telling us where we can visit and for how long. Also, what subjects can be discussed and where we can go in her home.
My mom lives with me. I love it when siblings come to see her, but I do like them to let me know ahead of time. My siblings know better than to snoop through my study or my room, but if they didn't I would say something.
But to answer your question. Is your aunt competent? If so she can appoint anyone she chooses as her POA. You could file for guardianship and might win but might not and then be in worse shape. You could also ask aunt to appoint you and or your siblings as her POA. My Aunt has only ever agreed to have one other nephew to be her POA and that was at my insistence and he was secondary to me. He died and she replaced him as secondary with my husband. I wanted a blood relation involved and I wanted a secondary but that was just my request. It’s not required.
Believe me, no one wanted the actual job.
No POA document I’ve ever seen could prohibit you from visiting or speaking freely with aunt but there are many posts on this site where POAs have prohibited siblings from seeing their parents or even knowing where they were. There is that old saying that “possession is nine-tenths the law”. Not saying your aunt is property but if you look this up, you’ll see it feels true.
What you need is a certified elder attorney to advise you and an agreeable aunt. If her nieces and nephews talked up NH placement etc or other actions that were frightening to her in the past, they (you) might have scared her into this action. What happened to your parents or other people she knew intimately may have been a cautionary tale to her. I assume none of her siblings are living? What about church or friends or neighbors that might fill in the blanks on how this person gained control of aunts POA?
I would visit often and take photos to satisfy yourself that she is doing well.
I can walk into my aunts home and within a few minutes know what’s going on and how she is doing.
It would bother me if my aunt did what yours has done but it is her right.
If you don’t think she’s competent or that the POA is honorable then don’t delay taking action.
Many attorneys will give a free initial consultation.