How to go about getting power of attorney over sister-in-law who has no one else to care for her?

My friend is trying to oversee her sister-in-law who is highly unresponsible, living in a hoarding situation, abusive with language and physical gestures. She has been turned down by group senior care and rides her scooter to buy hamburgers every day at the bar nearby. Any food donated to her has been dumped out on the lawn in her yard. My friend is paying all her utilities and property taxes, takes her to the doctor, etc. She has no other family. She possibly has some dementia, is writing checks and changing her accounts around at the bank, ordering things she does not need, etc.