I remember my dad, years ago, talking to their ( my mum’s and his GP), because she was acting strangely. I know this because I sat and talked to dad about the fact we had noticed she wasn’t right. Won’t go into detail, it’s irrelevant, but suffice to say, the GP was very helpful, and told my dad it could be related to medication she was taking at the time. There may have been more discussed, but I just left it there.
My dad died a few years later, and I became estranged from my mum. We’d never seen them regularly before, perhaps once or twice a year, due to distance mainly. I never felt my mum was right though, and could see it at each visit, probably because I didn’t have the ‘ drip drip’ of seeing them regularly. I never got the chance to speak to dad again, my mum always got in the way, so can’t say how it panned out.
Confidentiality may be more strict now. This was about 20 years ago. As I always say on every thread I go on, the only way forward is honesty, and talking. Nothing covert, just plain out there. The OP’s husband could be ill, but this neighbour needs to be informed. Even if she laughs and scoffs, the right thing has been done, and then you bettina, can concentrate on your husband.
All the best.