Well, this was an interesting set.
I might not be KirbyKaze, but I noticed a few things. My friend's a marth main so I am starting to know the match-up.
You have way too many SDs. I know this is not quite "tactical" but in the end it is, because I play Peach mainly for the fact you rarely "give yourself" to the other with an SD, unlike the spacies, falcon, or other quick characters. So yeah, don't miss out on those up-Bs and stuff, to not give a life to the other. Peach is hard to kill for Marth on nearly all stages, so dying like that gives a huge advantage to him.
Also, you have problems edgeguarding his Marth. He DI's fully upwards, which means an edgehog will rarely get the kill, which you understood as much. But he has to recover nonetheless, and you prevented him from doing so about 1 time out of 10. Observe him, figure out when he will double jump for that is critical. A marth who used up his double jump is much, much easier to edgeguard. I see you tried a few times to float below stage and nair, and though it missed, it was a good try. Mix it up, what Marth does to recover will depend heavily on what you do to prevent him. Put pressure on him when he tries to recover from high so he has to go for the ledge, so you can go for the lightshield-drop ledgehog. Don't automatically throw your turnips to edgeguard him, cuz as I said, the Marth is closely looking at you so if you mix up the throw time it will be harder for him to evade it. When you see him double jump, that's when you can float below stage and nair, or throw a turnip downwards, etc.
Uair him more, you want Marth above you not under you. I see you Uair'd him a couple times, which is not enough. I know he was DI'ing good but still, you never used dtilt which is a good move and spaces you well against marth, and leads to good follow-ups if he doesn't DI well, like 2-3 uairs.
Also, I see you tried all kinds of things against a high-percent Marth but uair will almost always kill him quite fast because those Marths DI upwards because of their recoveries so you could be surprised what results uair can yeild at high percents.
at about 8:30 you hit him twice with your grab before forward throwing, which gave him a lot of time to DI upwards the fthrow, while a quick fthrow can sometimes take a Marth by surprise, and his DI sucks and so he is forced to recover into a ledgegrab and waste his double jump, so you cna edgeguard him quite efficiently. All because of a quick fthrow, so keep that in mind!
Also, don't shield-roll into a Marth, unless you end up behind him. You did at about 8 min 30s and I think you died from it, not sure, but it cost you a lot of %
Grab Marth more. Dthrow can lead into another Dthrow if Marth doesn't DI away (and they often DI upwards by reflex so it works sometimes), and if he does you can still techchase and put more pressure with a spaced dtilt (dash attack, fair don't work if he's quick). UThrow puts Marth above you, which is exactly what you want. Instant Fthrow can lead to edgeguard, so it is good as well. Peach has a good grab range so use it, even though it's not as good as Marth, it's still good.
In the end, I think you're doing good but those SDs mixed up with the poor edgeguarding cost you the set. You gotta work on that. And use uair more, keep Marth above you.
