One neighbor bought a house from an elderly neighbor who had a reverse mortgage (she was about to loose it and be homeless) they allow her to continue to live there for free. Her health is declining. So now the neighbors do all of her shopping and cook her two meals a day. She refuses to leave her home for medical care and won’t let anyone else in but them. There is no family. They are concerned they might be charged with elder abuse even though they are doing everything to help her.
I would say that the neighbor should perhaps report this entire situation to authorities. By that I mean the APS (adult protective services). If there is none nearby to you I would consult a local county sheriff or the police.
This may be a matter for wellness checks. You say that the neighbor doesn't wish to go for care of any type. That may be a valid choice, but if the neighbor is mentally failing in any way, and the neighbor is enabling an unsafe situation here, that is more than any neighbor can/should take on.
The legalities of this home sale to pay off the mortgage on a home, whether the neighbor was competent to make such a sale, whether the neighbor was/is acting as POA for this friend/neighbor, all seems kind of up in the air. I think the important thing now is a simple wellness check on this woman essentially at risk because she is living alone, perhaps unsafely, and with only a "neighbor" watching over.
I would make a call, were I the neighbor, to APS and ask for a wellness check, and for options and pointers on this situation, which surely is going to get worse as time moves on.
Then ask to talk to a hospital social worker to discuss the fact that she has no family, no PoA (that you know of) and no one who can legally help her. It's possible she can go directly into a facility. Resistance, stubbornness and paranoia are hallmark behaviors of early dementia. Nothing can be done about it.
A judge assiging her a court-assigned legal guardian is really the only solution for her going forward.