I don't care how smart she is, she can't defy the laws of physics. Also, the reflection and harmonics are going to drive any animals and/or children & teenagers nuts.
EDIT: Unlikely. Children hear better in upper ranges, not lower. And animals are unlikely to be too perturbed. These types of noises are generated naturally all the time.
The challenge here is the engineering. How precisely can you build the tracking? How much leakage is there? Are there problems with harmonics? How do you build an app that can relatively reliably 3d position a device relative to a base station. And finally, how do you get that base station to be able to simultaneously or rapidly re-aim itself to target each of the devices. That's hard, but certainly exciting and very possible.
A directed, concentrated, high decibel volume, in the 40-60kHz range is not the sort of thing found naturally 'all of the time.' As other posters have mentioned, transmitting energy via sound is likely impossible do both safely and at useful amperage. Ultrasound is not safe at high energies even if you can't hear it.
[1] patentimages.storage.googleapis.com/pdfs/US20120299541.pdf
The fact remains that Ultrasound is not an efficient mode of energy transmission [1]. Wireless induction is almost certainly more efficient over the same distances. And ultrasound is a potential nuisance and hazard to wildlife and pets in way EM broadcasts simply aren't.