Coerced to change Medical POA

My grandmother lives in Wisconsin (my family lives in CA) and my mother has been her medical POA since 1998. My mom's sister has been trying to have my mother turn over the power of attorney to her (my mother is the oldest child and has been the legal POA for 8 years).

My aunt, who has stolen from my grandmother's home after she became incompetent from alzheimers and vascular dementia, has been trying to be in full control of the estate, money, and medical POA.

My mother was informed last evening that a doctor claimed she was competent enough to sign a new medical POA form, which my aunt coerced her into doing. Today, my grandmother does not remember signing any forms. In March, she took a test which scored her in many of the lowest percentiles for competency, and it was said she was as competent as a 3rd grader. Now it's believed she has the IQ of a 3 year old.

On top of all this, there was not a phone call or email to my mother saying the POA was being changed to her sister's name. It was done in utter secrecy and coercion. A social worker is who told my grandmother that she should change the POA then and there. My grandma in her right mind never would've allowed my aunt to be her POA - my aunt is a selfish woman, even my grandma has admitted to not liking her. She is most unlike my mom and her brother.

So my question: Was this POA change legal? The doctor NOW declared her competent, yet today she remembered signing no forms.

If we were to take my aunt to court, would we have a case if it can be proven my grandmother was deemed incompetent in March?

Thanks for your help. You guys rock.

That is doubtful it is valid if she cannot even recall it. But you may have to file in court and have a judge rule if the family cannot settle this by agreement. Sometimes even the threat of going to court causes compromise.