Thank you! "Acoustical Consultant" sounds like the sort of person I am looking for. Glancing at a few, it sounds expensive though. But all I really think I need from someone is to document this issue so I can make it stop.
That is an interesting thought about wall speakers. That reminds me, when she first moved in last year, I could hear hear drilling in to all of the beams in the walls down there. I assumed it was for something decorative, but now I am wondering.
Also, interesting idea about hanging something from the ceiling. I've been wondering it it is vibrating too - if not, perhaps I could hang a hammock so I can get some sleep
but I don't want a giant hole in my ceiling.
And to anyone thinking all this is not possible, it IS possible. I even inadvertently built something myself during all of this that kind of does that. I was trying to mitigate the vibrations by introducing other low vibrations inside my room (such as in to a chair or bed leg). It's weird, when I run it, I don't hear any sound, and I don't feel any additional vibrations, but on repeated tests -on the people who are still alive-, the downstairs neighbor freaks out and starts slamming doors or blaring her stereo, or increasing her vibrations, or such. Tempted to just leave it running, but I don't want to be the a-hole. If I do try that again, I'll use white noise instead.
Edit: Also, this fake traffic track she is running is almost hilariously bad. Most of the time it tries to make it feel like there is a single truck strongly idling nearby, except there is no such truck nearby and we don't get such trucks back in this corner of the complex. (I once lived somewhere where this did happen sometimes). The idling sound is a perfectly smooth wave form with no roughness. The real traffic vibrations we get out here are a very low, rough, combination of dozens of distant vehicles at once.