I'm just gonna splurge whatever comes to mind, so this probably isn't gonna be too organized. WD with your shield up alot, if she d-smashes or f-smashes you can WD outta shield for a grab. Sort of like a check raise in poker, let her make the move, If she grabs, c-stick a downsmash with your other IC. When she's in the air, you dont wanna approach her unless you can come from directly under with up airs. Her kicks will tear you apart from the sides. When recovering you almost always wanna recover from below. When solo, you can avoid d-smashes if you sweet spot with Popo. When you have Nana, you'll wanna hammer squall from below and hope she doesn't doesn't cc d-smash. If You find yourself above Zelda while she's in the air, you can usually fast fall a d-air or b-air. Zelda's up air isn't a very reliable attack. If she's on the ground, you probably don't wanna approach her. Her up smash will eat through what ever you have planned. You'll wanna avoid trying to finish with a smash unless you can either get below her and land an up smash or smash her out a dodge or up b. F-smash and d-smashes leave you too vulnerable to kicks. Most of your KOs will come from grab combos into smashes or ledge guarding opportunities. (Which is how it is with most characters anyways) Just avoid trying to throw out random smashes for kills. When ledge guarding you got 2 good options, desynch ice blocks and have Popo jump and shoot his ice blocks at a different height than Nana. This will force Zelda to recover in a more vertical path, giving her less of a chance to sweet spot. The other option, if you still have Nana jump out with a b-air. Make sure that you're fast falling onto her though. Don't try this if she's dropping onto you.
So let's recap:
Zelda's on the ground: WD with shield up, wait for a reaction and act accordingly.
Zelda's in the air: Try and get below her and use up airs. Don't force f-airs or b-airs.
You're above Zelda: Fast fall d/b-air if she's also in the air. Avoid if she's on the ground.
Zelda's off the ledge: desynch ice blocks. ff b-air.
Avoid wave smashing. Hope that helps