I too agree with putting a lot of miles on. Experience is key! Just take trails that if she does spook it doesn't put either of you in too much danger. (I know spooking is always dangerous but I just mean not riding by barbed wired fences or on cliffs and such
). It is awesome too however that you are working with her off the trail as well! That's still experience!
Just a thought, for the leaves maybe try taking her where there a bunch of leaves (maybe even rake some into an area) and have her walk through them. Then have her stand bye the pile and have something (a stick, rope, whip) and jiggle it in the leaves to make them crackle and move just a little. Eventually as she gets use to it you can intensify how loud and crazy you are making the leaves move.
It sounded more like she was afraid of something just moving around her on the trail though. So I'd also try maybe rolling a soccer ball size around her? You know start it off far away and as she becomes more comfortable move in a little closer as you see fit. Then maybe you could even change sizes of the balls to like a tennis ball, base ball something of the sort.
Also just holding a rope and walking around her while dragging it. Of course you wouldn't want it attached to her, or to the point she could get tangled in it, but it's some kind of movement! Maybe eventually letting it swing very lightly around her legs just so she could feel something touching them.
Haha sorry this is getting long, ideas just keep popping into my head. I like tossing things around my horses too. Like picking up a handfull of pine needles and tossing them into the air above us letting them rain down. Tossing a rag over their back so they can see stuff falling around them. I don't know, you know what she needs work with and these are just suggestions!
Everyone has wonderful advice! I love this forum! Just remember, baby steps and lots of praise for showing intrest!