The Peach matchup is one you have to treat delicately. You can't just throw stuff out and hope to catch them off guard too often. Your spacing in this matchup needs to be pristine otherwise they can catch you with an instant neutral air or that oh so dreaded down smash. Neutral airs for the spacing game will be your best friend as you can hold them out of range pretty well with that, and if you catch them even with just the first hit of it you can sometime get in on them. If you can get a grab you can get a lot of mileage on them. If you are at a stage with platforms, you can possibly bring them to 0-death or at least high percents. If you want me to elaborate on what I specifically do for that let me know and I can maybe provide a video of my combo if one was recorded lol. Also, the biggest thing and that goes for that Jigglypuff matchup too, never go off stage. There are times when it can be beneficial, but when you go off stage for them while they recover, it only will ever put you in a bad position and they can punish that really well. I hope some of this can be of help at all!