Use your speed to your advantage and try your best not to get hit. Dash dance like mad, jump around, wave land onto each platform as you do so to keep up your speed around the map. Pull away and dash back out of a approach if you read her Nayru's Love or fair/bair wall coming out as you approach.
If she gets you in neutral things can be very, very bad for you, so you have to make sure when you connect one of those hits, you follow it up. Once you learn how to SHFFL your Knees and other aerials I think you'll find Zelda isn't too bad of a MU for Falcon though it must definitely seem daunting for you at the moment.
As for her fair/bair, as yohoos, said, Dair works wonders. That said, try not to dish out Knees against her fairs/bairs. Her fair/bair will win practically every time as it comes out too fast and the PM developers made the Hitboxes for the moves absolutely ludicrous. Honestly if you play around her fair/bair and Nayru's Love, Zelda becomes a much easier MU for Falcon. That's most of what you need to fight her.
