Gray area, and would depend on interpretation of the governing body.
Probably not illegal since it looks like someone is connected to her left foot or ankle (hard to see from a distance and on the small screen of my phone) all the way up until she is no longer inverted, which happens at about prep level.
It looks like a very well-done flaunting of a couple of gray areas in the rules. I’d say it would be heavily event-specific on how the interpreters saw it at any given competition. You might take it to a regional and everyone be ok with it, then take it to nationals, and get a “no no.” I would definitely send a video of it to any competition where I planned to use it.
On a side note, I remember a rule where each competitor had to start with at least one foot on the ground. The opening stuck out to me more than that switch up.
ETA: all that stuff about the height of the stunt where she becomes no longer inverted becomes less of a factor now that high-to-High tick ticks are legal