Zelda's jab has no cooldown. absolutely none once it's finished. This means she can do something to your shield before you can put your shield down.
It takes 6 or 7 frames to put down your shield from the waveland and then to do a move. Yes you'll avoid the jabs, but I have the frame advantage to begin a dtilt lock, farores, or usmash (which will be close to destroying your shield), so it's slightly unsafe against her, though still a better approach.
I'm not too fussed over 5% really. But either way I seriously think it's just jiggs' weight that lets her down. If she were slightly heavier with that moveset she'd be fine =( Zelda's heavier, stronger in knockback, and too difficult to invade without risk. And her jab is underestimated. No one even stops to think about her jab but it's her super secret move, along with dtilt.