So I watched and stop motioned it. Look at how reversely extended her shoulders are…..it is ridiculous and I only know a few people who can contort their shoulders like that. That said:
I would try elbow hold aerial windmills first. Well, any aerial windmill. I know there was a tutorial or discussion on how to get into ballerina that way but I am too tired to go searching for it tonight. Get the windmill to ballerina/pretzel or whatever that is first. I would probably next work on that elbow/behind back grip and being able to hold your body weight just in that grip. Then baby step it….elbow grip to windmill, then add the foot reach around.