Is my Mom's 'paranoia' negligible or of concern?

My mother is 81, widowed 15 months (my father committed suicide), and is now living in a new state near my two brothers, in a beautiful independent living 'cottage' in a senior retirement place with all levels of care available. She is very sharp in many quarters, still reads novels, drives, and can hold a great conversation with anyone of any walk of life. Lately though, she makes comments that people are taking things that make no sense, such as the cleaning ladies possibly taking her (oddball) collection of cards, notes, etc, or someone is using her perfumes (which have evaporated over many years to dark stickiness), or drinking her scotch (which she doesn't drink), or even using her car at night. She is intelligent and sensible enough to know that it makes no sense that people would do these things, but cannot be disabused of these ideas. I've teased a little about people sneaking in, having a scotch, tarting themselves up with her perfume and writing their thank-you notes, and she laughs, but i'm not making headway. My brothers are a little more heavy handed, and she gets annoyed or angry. She was having some issues like this before my dad died, and she still holds to the idea that he gave a LARGE amount of money away without telling her (not really possible looking at records). So far these are not affecting her daily life, though she has mentioned people being in the house at night, 'but i lock my bedroom door.' She is generally very healthy, a little COPD, not too bad, gets vitamin B shots, and she is taking Ambien to sleep since my father's death. One of my brothers acts like she is 'losing it,' and the other says she's totally fine. I'm 3000 miles away. We talk a lot, and i visit quarterly. If anyone has any insight, I'd love to hear it. She doesn't fit Alzheimer profiles at all.