having poa of my mother, she having dementia, can she sign another person as poa without my knowledge? This is happening, and I have not been released of my duties and not sure when this has happened or taken place, another sibling has come in and is claiming that she has power of atty. with the permission of my parent that again has been dianoised with dementia.
An incompetent (in the legal sense) person may not be legally able to change the POA.
Your sister should have no problem showing you the document naming her POA. Start with that.