It's not necessarily that you should do nothing, but you can. For most of her launchers (depending on if it's CH and so on) there are certain moves you can do to get the frames at exactly +42 for the rebound.
For example, any stun followed by her 3PK launch (light and midweights only) can be followed by P then 46H+K for the exaxt amount of frames needed. There's more examples on the Pai forums if you want to check them out, or you can test some out in training for yourself.
So what your saying if I launch and do nothing and it says I got +42 I can do the juggle? Nice that it works on Pai considering she is the heaviest of the lightweights.
Yes, it does do more, but it only works on the "just frame" version of the rebound. If viewed in training, using 46H+K at a +42 launch height (in most cases) grants you an additional 2 frames to juggle with, making that juggle viable. It does the most damage out of any other combo I've found apart from wall damage from ending with PPKK
Oh my what a Pai. No pun intended honestly the first thing that came to mind. Also after 46 H+K in a juggle 33P+K, 6KP7K does more? Or was that for style purpose