Mom had dementia but all felt shse knew and she now regrets changing it from me to my sister because my sister has taken over her life . Was it illegal to go behind my back and change the poa?
If your mother has not been declared incompetent and she understands the concept of allowing someone else to act on her behalf, she can change the POA as often as she wants.
No, it wasn't really illegal if your mother made the change, but if she regrets that decision, then she can change it back to her. I'd take her back to the attorney if that's what she wants. Good luck.
Good luck.