I deal with Peach by being really careful. I either play Young Link or Fox against Peach because they have tools that allow you to annoy her from a safe distance, are mobile and can punish her pretty hard (mostly due to the mobility). Peach has insane pressure and punish games, so being reckless is not an option. Young Link and (especially) Fox both also can out-camp Peach handily (at least in my experience) and have tools to deal with annoying stuff (turnips). Fox is kind of a double-edged blade because Peach has a ridiculous chaingrab on him and has plenty of other tools to combo him really hard. Young Link doesn't have a lot of good, reliable killing options on Peach other than projectile --> dair, but his sword cuts through turnips and can keep Peach away if you space properly.
Something that makes Peach a little tricky to play against is that she's really good at taking a stock pretty much whenever she wants if you aren't cautious.
Well this post turned out a little longer than intended. I meant to just say that MTL Kyle's advice of exploiting Peach's critical failures is important, but you also want to be wary of her strengths. Peach has a lot of really nasty stuff. I like to deal with her by outcamping her and punishing her once she makes a mistake due to frustration with being camped. So far, it's worked pretty well. Peach being not particularly mobile works in camping's favor because it's easy to tell when she's going to try to approach or fake you out.
Peach telegraphs a lot of things lol
