How did you do that btw? I can't seem to do it... can she throw out a grounded move instantly?
You mean the grounded NL/DF from the ledge, right?
All you have to do is to press jump when hanging from the ledge and then input command for them
after she lets go off the ledge but
before she rises too high from the ground. The input must be timed correctly or else Zelda'll just ledgejump normally, but when you do it right her special moves stop all upward momentum she'd gain from her jump and make her kinda "appear" on the stage. With NL it's even possible to cancel all momentum before she reaches the stage level, so she'll just let go off the ledge and activate Nayru. The differences to normal ledgedropped one are that she starts the move from higher point and doesn't instantly start going down, so she doesn't fall as low and even her douple jump is enough to regrab the ledge.
The timing is really weird at first since you can't input the commands right after each other: there has to be a small pause in between. It isn't too hard, though, I can now do any of the things shown in the video constantly.
tl:dr: Grab the ledge. Press jump. Press B or >B.
Edit: For reversed Nayru's love from the ledge, it goes like this:
Jump=>direction away from the stage=>let go of the control stick=>B