Activating power of attorney

My mother in law (84) has been slowly deteriorating for several years. She recently had surgery on her hip to remove a screw that was causing her pain. She had to go to a rehab spot for a couple weeks but she came home Friday. It seems like her short term memory is even worse than before, until just a short while ago she hadn't eaten anything since being home. My wife and her brother think she shouldn't be living on her own anymore. 12 years ago as part of estate planning she created a power of attorney document giving power to my brother in law (which we're fine with) and my wife as a successor if he's unable or unwilling to serve.

Is there anything we need to do to activate the power of attorney? If we tell her that she can't live on her own and she fights us on it can we use the POA to do anything about it?

Thanks.

This is in Michigan if the state matters.