Camping is not what you should worry about; DF can trade hits with his arrows just good enough to make him want to approach you, not to mention Nayru's Love will further decrease his camping effectiveness.
What really threatens Zelda from Pit is that he can get you on the air, and Zelda sucks big time with an opponent below her. Get used to airdodging, shielding, and using FW mindgames to mess him up.
Pit is incredibly light, so you should have little trouble KO'ing him once you rack up some damage, which is the challenging part. Learn to DI well, or his abilities, namely f-b will mess you up.
If you also have the time, learn Shiek: He is faster than Pit and can combo the hell out of him before you transform back to Zelda and go in for the kill.