If Zelda is waiting for you to land (with usmash) or coming at you with a uair ready, just QAC away. Her ground speed is absolute balls, so she won't be able to catch up with you in time to punish the cooldown.
Protip in general vs. Zelda: Camp at mid-range, gg. Unless she perfect shields into a hyphen usmash, you can punish anything Zelda does to counter the tjolt on reaction. It takes some really good spacing, but once you figure out the distance, it's not hard at all.
Once you have the lead, sit back and lol as she tries to approach. (Hinthint: she has zero reliable approaches.)
Trust me, I play Zelda and do this MU often from both sides. It's hilariously easy if you play campy.