Lots of stuff to comment on, and this is only the first match.
0:14 This is an unsafe distance to use Din's. Instant Dash Attack from Bowser will clank with Din's and can hit you easily from this range. If Bowser is close enough, he will hit you and clank with Din's. If Bowser is out of range to hit you, he will clank with Din's and be at frame advantage in front of your face. Be careful.
0:16 Ftilt as an anti-air is extremely bad against Bowser when his aerials will usually beat or trade with it. Using Usmash instead would have hit Bowser clean. Also, Usmash combos into another Usmash at 0% on Bowser, and you get a free mixup afterwards.
0:19 Ftilt is a bad idea against Bowser on the ground as well. At that spacing, Ftilt could be punished by Bowser's upB OoS. Jab or Fsmash is generally better as a grounded spacing tool. It's harder for Bowser to punish.
0:23 Uthrow is generally a poor idea against Bowser unless there are platforms around. Even though Bowser has a blind spot below him, Zelda cannot take advantage of this easily on FD due to Bowser's air mobility and Zelda being extremely slow on the ground. A better option would have been to Dthrow Bowser and try to go for a mixup afterwards.
0:28 Unsafe Din's distance again. Thank God Riddle isn't using Dash Attacks.
0:33 If Bowser jumps at you, don't spot dodge on reflex. All of Bowsers aerials will lose to your Usmash with the exception of a spaced Klaw. However, Riddle was not far enough away to properly space a Klaw, so a Usmash would have covered all of his options. If he swings, he gets hit. If he spot dodges, he gets hit.
0:36 Unsafe Din's distance again. If you're going to do Din's from this range, try to use a retreating one.
0:37 Ftilt anti-air being used again. Usmash would have acomplished the same thing and covered more options.
0:41 Ftilt being used for spacing is again. If Riddle had decided to swing at you, your hits probably would have traded or Bowser would have won outright. Ftilt is also a bad idea against Bowser because it is easily countered by Bowser's Fsmash at that spacing. When in doubt, Zelda's Fsmash or Jab is always better then Ftilt.
0:46 You should have just Dsmashed him. It puts Bowser in a horrible position and is guaranteed. Trying to go for a LK is ballsy and honestly, usually won't work.
0:54 There was no reason to throw out this Din's. By throwing out this Din's, you let Bowser get back to the ground for free.
1:04 Again, Usmash combos into itself against Bowser.
1:06 It is a bad idea to chase an aerial Bowser when he has room to use Klaw. However, you could have just Usmashed and Bowser would have lost.
1:11 You could have been punished by UpB OoS here. Careful.
1:17 Unsafe Din's distance.
1:20 Yeah...
1:32 You had the percentage lead. There's no reason why this should have happened. DI toward the stage.
1:35 You should have waited on the platform for more invincibility.
1:41 This is a frame trap and honestly, it's kind of hard to avoid in a situation like that.
1:45 Don't be too ballsy with kicks that might not work. Usmash would have always worked in that situation. Because you went for the kick, you also set yourself up to get hit by UpB afterwards.
1:48 FSJFKLASJDLK:ASJFK:GH:ADSLH:KL
1:50 Be careful about rolling into Bowser. His UpB will beat anything you do, and can be a guaranteed punish to rolls at certain times.
2:00 LK is a horrible followup to Dthrow especially if your opponent knows to DI toward Zelda. It would have been better for you to stay grounded to abuse Bowser's blindspot underneath him versus going for a kick.
2:04 Airdodging into a grounded Bowser will get you killed. Never do it unless Bowser is lagging.
2:10 Smash DI out of this. It's one of the easiest moves in the game to SDI out of.
2:21 Bad DI on this Klaw. You want to fly into the corners, not the ceiling.
2:39 Should have used Bthrow and chucked Bowser offstage.
2:40 Again, kick followups off Dthrow are generally never gonna work against someone who knows how to DI the throw.
2:44 There was no reason for you to Fsmash again. Bowser would have either fallen or been able to jump before the 2nd Fsmash hits him.
Watch this to see how the matchup should go for both sides.
I know you've already seen it, but it's still informative. There's actually very little attempted camping in this video, because Zelda's camp generally doesn't work. Zelda vs Bowser is more of a zoning game; with Bowser trying to zone with Klaws and punish Zelda's over extensions, while Zelda tries to get Bower in poor positions and exploit him when she sees an opening. A premature decision to rush in for either character can get them destroyed, so it's extremely calculating.
Try to figure out when's a good time to use Din's. Also, look at my DI on Zelda's Dthrow. Kick followups simply do not work.