The point is, this was not based in fact. There was no such plan ever, especially with helicopters. Someone generated the bullshit, and we have to spend energy disputing it.
The NY health department does use helicopters to drop larvicide on likely mosquito spawning grounds[1]. Your mom did believe a false story and also there absolutely was (and is) a plan to use helicopters to distribute an an anti-disease treatments over NYC.
I think the tricky part of the misinformation we are all dealing with is that many elements of it (method of distribution, the idea of spraying down a city) are things that are happening in some way - the false narrative is the particular combination people believe in. I think it's part of why flat denials are often ineffective.
[1] https://www1.nyc.gov/site/doh/health/health-topics/west-nile...