My parent feels everyone is stealing from her, even those who are closest to her. What should we do about this?

Let them prove it. Sometimes in early stages of demetia they do feel everyone is stealing from them and they are misplacing things and money. Anna

I agree it could be the beginning of dementia being paraniod is often a first sign and you want to know what is going on so you can make plans on what to do about this.

If you feel that no one is stealing, and is possibly paranoa, or even an other issue, I would be in contact with your PCP or neurologist-as soon as possible, and get to the bottom of this matter.
Best. Hap

First make sure that no one is, then, try to find out why she is thinking that way. If being paranoid is new behavior it could be a sign of something else going on. My parents have always thought everyone was trying to steal from them. Thus, steel bars on the windows and doors, won't open the door to anyone they don't know for sure. They wouldn't let the visiting nurse in because she didn't look "right".......meals on wheels was sent away with a "no, thank you".
Good luck with your search.