If it were me, I would have had them make some sort of horizontal frame, with hand controls, with the tank mounted under, sort of like a laydown propulsion frame. Sort of like a full body seabob. [and as my body deteriorates, it sort of will be me]
Look, she obviously has some sort of topside help getting in and out of the water [and co-swimming] so strapping into a horizontal seasled is just as doable, and much more aquadynamic [is there an underwater version of aerodynamic?] IMHO.
My bet is she is going for the viral exposure deal [on top of being able to dive as I would assume she likes to dive.]