Stagger pressure or staggering refers to using pressure strings that have small gaps in them. The idea is that these gaps are large enough to prompt your opponent into attempting to escape in some way (pressing buttons etc.), but small enough that whatever they attempt will usually be beaten out by what you're doing or force them to carry on blocking if they know they won't win.
In Noel's case, things like 5A > 5A > 665A or 2A > 2A > 665A are the kind of things that you'll want to use for staggering, but you can experiment in training mode to find others normals and traps to throw into the mix. Like Sahgren pointed out, you'll want too mix this up with her frame traps and some tick throws to keep your opponent honest and don't forget that staggers can easily be beaten out by DPs.