Diddy Kong is a hit and run match up. Thus why you can Camp/time him out. When Diddy has a nana in his hand. Do Not rush diddy. Pay attention to what he is doing. Most people just wanna rush in and Dair or go in with Fair. That typical gameplay is not gonna work. Remember that his options are limited. When he has a naner. he can't use any of his stander attacks. When he does toss it go on about fighting him. But don't go all aggressive. Diddy will just Fair you every time. When a Naner is near you, Ground Float Nair near it and Drop. You will Grab it. So there is no need to dash attack it to get it. Kills times. Also you can do this if Diddy goes in for a dash attack to get it. This can hit diddy and you grab it.
Time Ground floated Nairs to grab the naners and toss it back. Or play around with it to do damage on diddy. So Can have both naners under your control. Also ground float alot. Both air and ground game grounded Plus a naner game from Peach. The Pressure diddy will be having, he can't do anything out of shield. And throw in Z drops in the mix. since when pressured, Peach has shield advantage. So all they can really do is side step or roll.
When you have naners under your control, get that tunip game in as well. Have a nair in from and behind you. or even on platforms for traps. and play around with your turnips. You have a wall along with Naners. And if diddy wants to get in. you have your spaced ground floated moves to turnips/naner set ups. he can have only 2 naers out at once. They will be under your control plus you playing with turnips. He now has his peanut gun that turnips go right through. he wants his naners? he has to go through your turnip and naner play/wall. Or wait for them to vanish Which you can take advantage of.
When Diddy has a naner, do not approach him. He can toss it all he wants. That does not mean you have to go to him. And you can catch them easy. They become yours and you start from square one. Get your hits from diddy and if you can't pound on him anymore, just get away. If he has a naer in his hand. You can wait for the toss or grab a turnip and hold it. Use that turnip to save you incase he goes in with something. But don't do this all the time. Cause it can limit your options to counter attack or break away.
I don't like being in the air too much. cause if he sees that basic Peach floating game, he will just go in with Fair I usually try to stay as ground as I an with Diddy. And limit my turnip use. I kinda treat this match up like Falco. Banana game with Peach+frame advantage= Diddy can't do ****.
Don't try attacking out of shield with full hop dairs or bairs. That Fair of his aint having it. If anything, Ground float it out of shield. Space it to a reserve jab cancel. DON'T BUTTON MASH OR PRESS A SO QUICK. characters can side side her double jab then punish you. This helps if he wants to side step or roll. Then you can catch it to a punish, or just run.