Mom is in assisted living and taken care of well.
Sibling has healthcare POA and financial POA but declared bankruptcy and has gotten money from Mom over the years, $10000 one time, and never paid her pack. I know it's Mom's money and she can do what she chooses with it, even if she does have beginning dementia. Sibling convinced Mom to give her control over everything, and sibling has always been a private person and works 'alone' and does not include either my other sibling nor I on decisions.
Sibling has always been able to manipulate Mom and make her feel sorry for her for whatever trials she's going through in life, and how to get sympathy from Mom. After our Dad passed years ago, it just got worse. The worse luck my sibling has, the more pity my Mom feels for her and Mom told me 'SHE NEEDS me'. Whereas my elder sibling and I have never had to run to Mom for help and have just been able to enjoy our time/relationship with her. Mom still does NOT understand how hurt my older sibling and I were that she didn't give us ANY legal authority, NO legal voice by turning everything over to our sibling. She said she just wanted to 'make it simple'. We did ask questions at first and had family meetings, but nothing came of it. Mom doesn't understand all of what is in those legal documents. Mom's POA had a clause that she WAIVED the POA's responsibility by our state law that the POA had to report financial statements/recordings on how her accounts are handled. So legally sibling doesn't have to tell ANYONE squat.
do something. I don't know what your mom's mental health is like now, but if she's able to understand what's going on then you've got to decide what to tell her. Some parents like to be included in their own financial affairs, some don't care. Soon it'll be too late to tell her anything cause she won't remember it anyhow.