General Power of Attorney: Sister-In-Law Has Power of Attorney Over Mother-In-Law

My question involves a power of attorney in the state of: Florida

My best friend's (I'll call her Kat) mother ("Lucy") lives in an assisted-living facility in Florida and suffers from dementia with periods of lucidity. Kat's brother ("Frank") held power of attorney over their mom until he died recently of cancer. Frank's wife, "Joan", has never been what you would call a friend of Kat's. Kat recently found out that, somehow, Joan now has the POA.

Kat would like to have the POA herself, since Joan has been doing things that Kat's mother wouldn't approve of, such as giving away furniture and such out of Lucy's home, which is willed to Kat and Frank. This has been confirmed by other family sources.

So, doesn't the original will supersede the POA. And is there any way that Kat can petition a court to revoke Joan's POA and have it revert to her? Does Kat have any legal recourse as far as the items that were given away without Lucy's consent

I'm just trying to help out my friend. So please explain as if I'm a 2-year-old. lol

Thanks to everyone for any advice you can give. If more info is needed to formulate a better answer, just ask.

General Power of Attorney: Sister-In-Law Has Power of Attorney Over Mother-In-Law