I don't know of any very young American aerobatic pilots, but I'm sure they're out there. From a competition standpoint the best female American right now is Patty Wagstaff. She flies an Extra 300 which is a German aerobatic monoplane. She is very good, but Svetlana Kapanina has beaten her on an almost regular basis in world competition. Kapanina is famous for her over the top, completely out of airspeed, maneuvers while maintaining total, perfect control. About the only other pilot on the airshow circuit that can do a low altitude prop hang besides Kapanina is Sean D. Tucker. His highly modified bi plane is all but specially constructed for it.
It's one thing to be able to simply do these maneuvers, let alone do them at low altitude. At the low altitude she and others perform at there is zero margin for error. Bill T.