What to do about mother-in-law lying, outsider meddling?

My mother-in-law, who will be 88 in September, has early stage dementia. My wife (we've been married 7 months now) is her legal guardian and financial conservator - the third person to hold that position over the past 4-5 years or so (the first was my wife's cousin; the second was a professional company called "Connections"). My wife's cousin first got the conservatorship after my mother-in-law fell for the "Jamaican lottery" scam, sending tens of thousands of dollars to the con artist. She also swore that the con-man "loved her" and she was going to get a passport and go to Jamaica and marry him there. She would not even believe the county sheriff when he tried to tell her she was being scammed (they were investigating a money-laundering scheme the scammers also got my mother-in-law involved in). In fact, she STILL thinks she won the Jamaican lottery and thinks she is being "punished" by losing control over her finances. The cousin was granted guardianship after my mother-in-law fell outdoors in the wintertime and barely managed to crawl to the house, so he decided it would be best to move her to an assisted living facility and to sell her house so she would have money to pay for the assisted living facility. (Incidentally, the only reason my wife didn't have the position of guardian and conservator first, instead of her cousin, is her abusive and controlling ex husband would not allow her to do anything to help her mother.)

Connections took over when the cousin moved to Florida. When my wife was abandoned by her ex husband, and she divorced him, she requested the guardianship and conservatorship. Her mother complained constantly about how things were at the assisted living facility (she got stuck in the elevators twice, got run over by another resident on a scooter, and spent most of her time in her apartment despite efforts of staff to get her to participate in activities). Also, her money was running out at an astounding rate - up to $5,000 a month spent on rent and a "visiting angel". My wife got permission from the probate court to use her mother's funds to buy a house where she could take care of her mother (several hours' drive north of the assisted living facility). The mortgage is under $1,000 per month, and she pays rent that covers nearly half of that, thus helping to preserve her mother's assets.

Now, my mother-in-law calls her old friends up and complains that this "isn't her house", says she doesn't have a guardian, swears that God promised she would have her old pre-assisted living house back miraculously, says she has a "boyfriend" who will come here and marry her, and claims my wife is "spending all her money", despite the fact that as conservator my wife is required to keep detailed records of expenditures. One or more of my mother-in-law's friends have even sicced the Department of Human Services on my wife. Despite no evidence of wrongdoing, they continue to hound my wife, even trying to convince her to turn the conservatorship over to someone else (my mother-in-law thinks she should be able to handle her own money, despite her inability to do so - she gives all of her allowance away to various TV ministries: sometimes, the same one several times in a single month!). The DHS agent came by again today, and my mother-in-law lied to him and told him that she had fallen down while my wife, my mother, and my kids were out celebrating my daughter's birthday on Saturday (my kids are from MY last marriage). She told us on MONDAY that she had fallen, but I call BS on that as she would not have been able to get up on her own, and she was getting around just fine with her walker (as usual) on Sunday. SHe has a long history of lying to people to get her way or to gain sympathy, and then the people she gulls cause trouble for us. What can we do about it?