As my MIL's dementia  progressed  we decided to open another  checking account for her.   We called this other account her  "business account".   We deposited her farm rent checks  in it and paid her   farm expenses out of it.     She never even knew it exsisted.   She carried her  checkbook   that her Social Security came to.   So she had the ability  to write a check at church....  But,  it never had more than  3,000 dollars in it.     If it got that much  I paid the  Assisted Living  bill with it.  

We wanted to prevent a scam or out right theft.   She was a very trusting  soul  and if someone had walked in and said,  "you haven't paid your bill here"   "if you don't pay  $XX   you'll have to leave" .    She would have written them a check on the spot.     

In the last year  we never took her in new checks.    We took her in cash once a week.   There was a note in the checkbook that said call Tom  or Sue if someone needs a check. 

We did all this with the blessing of my husband's siblings.