The main reason that I believe Zelda does not win this matchup is the difference in speed, both in movement and attack frame data. Fox has good combos and can rack up damage on Zelda effectively. Fox can no longer get his kills from the double-jab, but unlike what Skarfelt said, Fox still has good kill setups. Fox has an up air confirm off of a side B right above the ground (after falling down or a SH), and the blaster can bait out Nayru's love, or it can pressure Zelda's shield/force her to find a new option. Fox has no trouble stopping Din's Fire by shielding or perhaps shine? (needs confirmation). Fox needs to be patient when Zelda is at kill percent, and either bait Zelda if she exploits shielding, pressure her with blaster fire, or just grab her. If the Zelda is not shielding, Fox has a super-fast f-tilt which will allow for a tech chase with either up smash or down smash, and when a Zelda is falling down onto the ground with a Fox running at her, (a little tip) she will LIKELY tech roll away. They may try to mix it up, but once you get a read correct, up smash kills Zelda very well. And if the Zelda player holds shield and you get a grab as Fox? Take it back to Melee. Up throw to... Well, up air doesn't quite get the confirm it used to, but if you bait an air dodge, you can get an up air, and if the Zelda jumps or tries to come down with an aerial, she is in a disadvantageous position.
Now, an offstage Fox is in a really bad spot, so the only thing I can really say is to mix up your recovery. Recover high, straight over, and low. You should use all of Fox's specials, the up B and side B for obvious reasons (and DO NOT side B right onto the stage, go to the ledge or under the stage if you have a second jump), the blaster can be random enough to cause an on reaction shield/Nayru's love, and shine stalling is very important because Zelda can jump offstage, but will need to recover shortly after.
After getting the grab as Fox at kill percent, there are two good options, up throw and throwing Zelda offstage. I already covered up throw, but when you throw a teleport-recovery character offstage, they can recover high with their jump, or they can teleport to the ledge as their main options. If Zelda recovers high, Fox has faster aerials. Try your luck with an up air if the Zelda is right above you, create a wall with forward air, or swing the back air. It is very important for any Fox player to be able to land a back air, especially I'm this match up. Back air is a kill move and very strong for sending characters far offstage. Learn to land it precisely, especially on a relatively large character like Zelda.
If they recover low, you have three good options.
1. Read the get up - very self explanatory here, and fAir covers most options.
2. If you can down smash during the one frame, do it - Zelda's teleport will always make her snap to the ledge in the exact same way.
3. Ledge trump - you might be able to bAir or nAir, or, as I mentioned before, Zelda can teleport predictably to the ledge and get down smashed due to the lack of invincibility, or recover high, which is also predictable and Fox's superior aerials should let you get a good edgeguard.
For everything good that Fox has, Zelda has a Hoo-hah against him, and many other good tools in the matchup, and overall, without double jab, it's about even due to Zelda's edgeguards. I probably should have posted this on the Fox page, but I hope that Zelda mains will see what tools Fox still has that they need to watch out for. The MU is doable for both sides, and I hope that it encourages either group to improve their skills to outplay the other. Thanks for taking the time to read all of this!