My mother-in-law has not been diagnosed but is getting worse: leaves cook stove turned on, loses her meds, gets very contrary, accuses husband of cheating (85y/o), has open water bottles all over the house, always talking about dying, can't hear well, thinks she's being talked about. I think she would be too contrary to submit to any kind of psych test. Thanks
With the family in agreement, I'd get mother-in-law to doctor, letting the doctor know what she has been experiencing. Based on the diagnosis, the family can explore what options are available for her care, if it's dementia.
Is her regular doctor someone who just looks at blood tests and says " she's fine"? If so, you need to find a geriatrics doctor who will listen to your wife about her mom's behavioral changes.