ehh, i'm not all that good when it comes to all the complicated logic and stuff etc, but i'll try my best to help
Zelda as a opponent is pretty bad in most ways, strong movesets and reasonable speeds going to have you on edge mostly
Firstly, her standard B can counter projectiles, so your turnips won't do much unless you can catch her whilst doing a din's fire, however, with good timing, you should be able to get her before she gets you
Din's fire is excellent on levels like FD and port town, where you only duke out on one platform, she can camp with it as well, and if hit accurately, can do a fair bit of damage,
if you're going to go offensive, you should try to watch her back off, she might go in for a din's fire, if so, quickly float and choose your attack position, retreating against a master of timing isn't wise as this attack can be fatal if done correctly
i'm not 100% sure if toad can actually reflect some of din's fire, if this works, you can use the attack to your advantage, especially if they rush you afterwards.
if you can time it right, peach bomb or forward hit (not smash, you'll be left open) her if she gets careless and gets too close.
if you're too afraid to get close, time the turnip throwing and coax her to use din's fire, time the jump and throw correctly, and you should get her before she has time to neutral-B
i don't know if any of this information is actually of any use, i'm not a veteran when it comes to advice, but there's a first time for everything. if it is helpful, good