Early signs: jealousy and paranoia? Anything I can do?

My grandmother had dementia, and more recently my mother has been having some odd behavior. When she visits, she says that the neighbor across the street is nosy and often watching us. She also says the neighbor next door, who is a single mom, is trying to steal my husband. A few nights ago, I hired a babysitter to help watch my kids while I attended an online class. She insisted that the babysitter and my husband were flirting (“he walked very close behind her”).

I think these are delusions and personality changes that could suggest dementia but my husband doesn’t think it’s dementia as she’s otherwise all there. I’m wondering if anyone else has had this experience and how they addressed it. I tried talking to my mom and she screamed at me that she won’t be visiting anymore. If this is dementia-related and out of her control, I want to know how to help.