I mean I think she’s driving herself bonkers. The real issue is that she just needs to let it go. In time, if she really is hearing a high frequency, or if her wild theory is true, they will give up or her hearing literally will. I was 34 exactly when I could no longer hear that frequency. I used to test it a lot back in the day. Was fun. Anyway. Even if it’s real, it could be any number of things. Power lines, some appliance, tinnitus, atmospheric pressure (try opening a window) etc etc. I am surprised you didn’t cut the main breaker and shut off your phones just to see if it persisted, or go see a doctor. I would want to rule that shit out asap. Schizophrenia doesn’t generally hit people that late in age, (unless it’s amphetamine induced) but it can occur in the early 30s though far more rarely. Onset is usually 18-25. So doubt it’s that but I am not a MD. Does she take any prescription drugs like adderal? That shit will drive some people mental. It’s just legal meth. IF you wanted to record it, just to see if it actually is something so high, or low you can’t hear it, you will need specific microphones to properly record some ultrasound and especially so with infrasound. Anyways sorrry. Sounds like a real nightmare to go thru. I’m kinda hoping it’s a drug and she can bin that crap. The paranoia is what’s concerning. Good luck.