Hey. Sorry this took awhile, I'm on vacation.
Olimar can do quite a bit to Peach if she's just floating. Aerials are good if she is approaching you, just run up and beat her to the punch, almost every Peach is an idiot and tries to approach Olimar with fair all the time and her fair is quite slow. His fair works well. His nair works well also, it has alot of priority, you just have to be close and you won't always be close obviously.
If she's timing you out with float and killing your pikmanz with aerials that is more of a problem. Honestly I would just start farming for purples if she isn't going to approach, you can annoy her alot more with those and use them to help you approach - use them like peach uses turnips - throw one, make her hit it with an aerial, follow it, hit her during her lag.
tell me the specifics of what you're having trouble with and i'll tell you more (if this post doesn't help at all.)