*pre-emptive apology for ramble/lack of formatting*
Zelda is a bit more commitment heavy than characters like fox, so this is definitely a rough situation.
I find that establishing a deterrent early on will give you some breathing time. By this I mean SHOW the opponent that you can control farther than they think. Things like wavedash fsmash/ftilt when properly spaced are fairly safe but hit a huge area/a respectable area. Suddenly the opponent, even subconsciously, will dashdance a little farther or a little wider. This breathing room gives you the little Yomi decision of either 1)them committing and you playing defensively (zelda's defense is GREAT) or 2)them not committing and you placing a din.
If they commit wrecklessly, opting for USmash OoS (hits on frame 2. FRAME 2), drift back fair/nair, wavedash back + ftilt, fsmash, even uptilt if you really read their approach (thanks intangible arm!) all work wonders. Remember that a large portion of your ftilt sets them behind you and, for most the cast, in a beautiful position to eat more sparklemagic. This makes Zelda at the ledge somewhat less of a trouble. If you are losing space frequently in the fight, remembering this option can put them exactly where they don't want to be (offstage) with a din in front of them to deal with as well. Also if you're getting pressured don't forget teledashing to the middle of the stage! It's pretty safe if used sparingly and can be used as on Oos option when you're really feeling the pressure. Another defensive option is a drift back din.
If they don't commit or dash back a bit to far, SET THAT DIN. RIGHT NOW. That thing is your life blood and gives Zelda what she needs to make up for her *ahem* lackluster normals. The din is all about controlling the pace of the game and tempo reversal. Anytime you can safely set a din, it's probably worth it as it makes her able to pressure her opponent much more safely. It doesn't even have to hit. It just needs to be a scary looming fireball and, what do you know, the opponent jumped to avoid it and can no longer dash or use any ground moves and is subject to their probably-not-great air control speed (which tends to be the case for the super speedy dashers!) Their options are limited and that just makes you stronger. Plus zelda loooooves people above her. Uair and Usmash make quick work of mostly-vertical approaches and utilt stuffs basically everything if you read it right.
Also, for both offense and defense dont forget your wavelands. I have some more testing to do, but all of Zelda's aerials barring uair finish in time to waveland. Fair and bair might require some interesting fast fall timings, but it works! And just for offense, don't forget the potency of your nayru. It can cover your unsafe SHFFL approaches by making them think twice about shield-grabbing. Once they get used to shielding nayru, toss in some grabs :]
Happy Sparkling! (hope this helped at all haha)