Cadence is currently visiting Club Penguin for the 2011 Puffle Party. If you need help finding her, I recommend you use my Cadence Tracker.
If you need help finding her, she tends to be on the Nightclub Roof.
If you find her, you will unlock her stamp as well as get a background from her.
Cadence usually visits crowded and popular servers such as Abominable, Alpine, and Sleet. However, she can and will sometimes visit less populated servers – however when she does, word spreads quickly and the rooms fill up with penguins trying to get her background and stamp. Good luck!