M.W.
So sorry about your MIL. Both of my grandmothers have dementia. One aunt was able to get POA while the other one wasn't because my grandmother is very stubborn.
It is a lot of work and you really have to keep an eye on persons suffering from dementia. Once, one of my grandmothers walked out of the house, stopped a guy walking by and told him to call the police because the man inside wouldn't leave and her husband was on his way home. The man inside was my grandfather and had a very hard time proving to the cops who he was. Grandmother is in later stages of dementia but at that time, she was cunning and there were no clear signs to a stranger that she had dementia.
You may want to look into some adult day care services to help her get out of the house from time to time. There's also a lot of services available, just search online.