Zelda's an odd character. She can really abuse Falcon's fastfalling at lower percents and take advantage of him being forced to approach her.
Personally, what I do is keep close to Zelda while being defensive and shielding almost consistently. A lot of her attacks have range and lingering hitboxes, but it's possible to get within her comfort zone. Try to keep within distance where she won't have the time to cast a Din's Fire without being punished, that should be common knowledge. Try to bait attacks out of her and don't risk doing anything that could get you punished like Raptor Boost or Falcon Kick because she does have priority and options to punish.
Critical Heel is a lot like our Knee of Justice, except she's more floaty than us and it's a bit more predictable. Though, correct me if I'm wrong, she can buffer a Fair or Bair while short hopping next to us an it's possible to land a sweetspot before she even reaches the peak of her jump. I'm almost certain that it's been done to me in the past and that I've done it myself as Zelda, but against Falcon... I'm not certain. DK, Ganondorf, Bowser and ROB, I've done it on for a fact. So just watch out for that too.
Nair, Dtilt, Usmash, Dsmash and Nayru's Love are some of the other things you have to watch out for. Priority and range, eats through most approaches and attacks and can pressure you away. They're difficult to punish, too, so watch out for those and try to space with either aerials or utilt frequently. For aerials, I would say to use Bair or Uair more preferably. They auto-cancel immediately and can keep her knocked back.
Her recovery is where she fails. It's one of the easiest recoveries to punish next to Lucario. If you know where she's going to land or if you're on the ledge and she's force to recover on stage or in the airspace above the stage, you're almost guaranteed to punish her with a well timed Knee.
