Sorry, just to clarify further, there’s never really a point where the movement is “only” one thing or another above or below the string. There’s always overlap of some kind, otherwise the hand would need to make an instant directional change and that’s really not possible. The amount and nature of the overlap is reflected by the arm position. In a parallel setup, you can do a pure deviation movement over the whole range of motion. And in a 90-degree setup - either supinated or pronated - you could have a pure flexion-extension movement over the whole range. They wouldn’t be crosspicking because pure wrist crosspicking would not be possible at those orientations. But these are the inflection points.
At every point in between those inflections, you have a blend of RUD - radial ulnar deviation, to use the academic abbreviation - and FE. In the case of Steve Morse for example, he’s toward the supinated end of the spectrum, so in his movement, FE goes almost the whole way. RUD appears above the string. In Molly’s case, she’s pronated but closer to parallel, so deviation goes the whole way. But again there is overlap and FE continues a little below the string. If you were to pronate even further, you would eventually arrive at “reverse Morse”, where FE is going almost the whole way, but RUD now appears below the string. It’s fun to experiment with these things just to help you understand what’s really going on, but you can indeed “reverse Morse” and it sort of works.
In Molly’s case, again, she’s closer to parallel it’s going to look deviation-y. However she can indeed flex a little below the string because of this. And she may do that, along with a tiny amount of forearm adjustment to reach farther, such as during these back and forth inside picking type sequences.
Again, all of this assumes she’s using a wrist motion pathway. If she adjusts that to be somewhere between a pickups-parallel path and a wrist path, then you will definitely see some forearm involvement because the wrist along can’t trace that path.
