for a good understanding of the matchup.
Alright, although it may sound odd, I have to agree with Macchiato that this matchup is 100% in Zelda's favor. Get ready for a wall of text
Din's Fire is great at pressuring Rosalina (who thought I would ever say that lol) bc it provides slight shield pressure while also getting Luma out of the picture. Another great alternative is the Phantom. Nayru's also is really good as an oos option because it destroys Luma as well, and even if Rosalina can punish you her Luma will still be too far away for her to do a significant amount of damage. Even if she gets a dthrow at 0%, what's she gonna do to Zelda? Most of the time, even if Zelda DI's, the only thing that will be able to hit her is a fair, which isn't a big deal at all.
Neutral / Approaching
Zelda is going to spam Din's Fire (Brawl habits living on aw yeah) to shield pressure Rosa and get rid of Luma, which is going to either force her to approach due to her slowly whittling down shield, or allow you to approach due to the absense of Luma. In the neutral, I find Phantom is really good to completely stop her approach. If she does get into your area and tries to use Lunar Landed nairs, I'm pretty sure Zelda can do dtilt/dsmash oos before Rosa can shield.
To address approaching as Rosalina, roll past that Din's Fire. It's the only option that saves Luma from being obliterated. When I was playing Macchiato, I noticed that the usual approach of nair is not very good in this matchup. Zelda can easily FW past or into her, striking both her and Luma. I'd advice not using Rosa's nair too much in this matchup, but if you do just make sure you do it at the right time.
I wasn't sure what other section to put it in, but I figured it'd fit fine here: Zelda can use Nayru's Love to get out of Rosa's multihit jab
K i l l s (aka bye Rosa)
Zelda can do some nasty, crazy, disgusting things to KO Rosa, whereas Rosalina doesn't have particularly special KO options against Zelda. First off, Rosalina is one of the tallest characters in the game. In other words, LIGHTNING KICKS GALORE. From the center of FD, a LK kills Rosalina at 75 - 80%, whereas fsmash kills her at 90-100%. Pretty nasty right? WELL THAT'S NOT ALL. Albeit risky,
Zelda can KO Rosa at 60% with a dthrow to Farore's Wind combo. To top it off, I'm pretty sure that dtilt to a jump cancelled Farore's Wind is a guranteed KO combo at
50 PERCENT. Rosa's most reliable kill moves in this matchup are probably going to be fsmash to punish failed LK's and overall end lag from Zelda, as well as usmash just because that's a great KO tool for Rosalina in general.
Kind of related to kills: Two lightning kicks or two to three (depends on if they continue holding shield) sweetspotted dairs can break Rosa's shield.
GIMPS GIMPS GIMPS
Rosalina has her signature dair that either spikes or hits like a frickin train if Luma's hitbox connects. I've found Luma's nair and Rosa/Luma's bair gimps to also be very useful against Zelda. Rosalina will have to be extremely careful when recovering as
Zelda's dtilt reaches below the ledge and can pop her up, leading to some crazy dair spikes. (if the time stamp doesn't work for the video it happens at 2:20).
Something important to note that relates to the offstage game is getting back on stage.
Rosalina dominates the ledge while Zelda is trying to get back up, since Rosa players usually send Luma out to the very edge and place Rosa a bit away from Luma to cover options, I find that dropping down, jumping, and using Farore's diagonally downwards and into the stage is great. It hits Luma if it's right at the very edge of the stage, and if Rosalina is standing far away the reappearing hitbox will hit her.
This is one of the few top tier matchups where I feel like going Zelda is my best choice.
60:40
I've never really done a matchup analysis before but.. hope this helps.