It's as if she is telling it for the first time. My husband told her that he talked to a co worker about a specific restaurant and they liked it. 15 minutes later she told us the exact same thing my husband just said, we new she was lying, she does this all the time. repeating what me or my husband says.
Being armed with as much knowledge as you can use will help you and hubby understand what is going on with his Mom. Mom isn't lying..... she has memory issues.
Since she's in Independent living, I might check to see how she's really doing. One the dementia reaches certain stages, the patient may have difficulty without daily assistance, since they forget to take meds, bathe, eat, pay bills, etc. Eventually, she may need more direct supervision. She may not be able to tell you that.
But in the end, we take on the responsibility of caregiving for a reason. Deep down our conscience won't allow anything else. So, we dig deep and put one foot in front of the other. This will pass someday, and our heart will be content we stayed the course.
I'm guessing your mom-in-law has little to talk about. What's the harm?