Its a little something like...
http://www.youtube.com/watch?v=q_3gvnGatuY
from 0:34 to 0:39 and 1:57 to 2:04
But um... well i've posted this elsewhere a bunch of times try searching older threads or cort's thread but basically, the... ugh...
pillar (I dont like this name because it isnt as nearly a reliable sheild pressure as other characters have), is not so much about pressuring your opponent with attack after attack as it is pressuring them with guessing game after guessing game.
I should note that the below situations are assuming your opponent sheilds, if you land the nair there's not a whole lot of guessing just let the hit go or at low percents follow up with a dash attack (or infinitely more fun, more nairs
)
The float cancelled nair is a fairly low risk approach with peach, because it is strong, fast, and has little lag once you get it down right. But blindly going nair slaps nair slaps nair slaps is gonna land you into a solid grab, or allow your opponent to reset control of the match to neutral instead of having it in your favor by rolling away. What you mix up with your nairs is key, but the main component here is the use of the nair. Pretty much the lowest risk move is to down smash right after the nair because there's no opportunity to grab in the middle if done right plus you often poke through their sheild by the last hit or two of the d smash.
But there are so many other options which could lead to greater reward rather than neutral advantage to both parties and an extra 12 or so damage. I could quite simply use the nair to cross over and then bair them immediately, and then another aerial, or throw the d smash in there to keep my opponent off balance and perhaps trick them into a sheild grab while I am behind them. Doing the slaps is the basic counter for someone trying to blindly sheild grab. The second slap sends them away for you to dash towards them and reset this guessing game, or if they dont react quickly enough sets up for a dash attack combo, or whatever your fancy is.
But of course, what use is the double slap if they see right through it? something far more devious would be to do a nair, the first slap, and then grab while they hold their sheild up awaiting for the second slap that never comes. How about we forgo a followup attack all together and then dash away? You've been given a risk free turnip pull now, which can help your next approach. Perhaps you dash away only to dash dance back to them into another nair... perhaps a grab?
I hope this allows you to understand all the options at peach's disposal using the nair.