Hey, Peach main here popping by to give my own thoughts on the Roy matchup. Take everything I say with a grain of salt, as there may be a few things I am overlooking about Roy. Also, I am by no means a great Peach, I like to think I am good, but I'm not amazing.
I
personally think this is slightly in Peach's favor. From what I have gathered from Roy's I've played against, it seems like he has a good punish game, being able to get a lot off of a grab. This is good for you guys, as damage means a lot for Peach, since she's so light it will mean you need less opportunities in order to take something. Another thing that can be a problem for
me is the fact that your recovery has a disjointed hitbox. This means that I can't edgeguard against you by dropping turnips most of the time since you can just Ph1r3 through it.
However, I think our neutral game is equal if not slightly better than yours (I seem to be beating Roy's in the neutral, but this is very anecdotal since I have only played a couple of legitimately skilled Roy's). We have the turnip which can stop your approach. This can force Roy into a bad spot since we can dictate the tempo.
The things you want to look out for are the following. Our down tilt is a great combo starter, so do your best to not get hit by that. However it
can be teched on hit, which means we don't get anything from it. Look out for the turnips, we'll often shield and then punish a wiffed attack by tossing it into a further punish. Always be mindful of that.
I know a few Peach's (myself included) that will float a lot in the neutral. This is super punishable. Because we can throw out aerials on the ground, some Peach's drift in and out of your range with the float. However it is beatable, because they still have the landing lag from it. So if a Peach tries to floating fair you for example. Shield it, but don't shield grab, as they'll be out of range. Just drop shield and dash grab (or your choice of punish). If the Peach is floating above you, make use of your uptilt.
Finally,
do not sleep on the up-b! Our parasoll can kill stupidly early (especially on Duck hunt with the tree for example). So do not get hit by it. Also, the hitbox
stays out while she is floating down. So it can
still kill even if you just bounce of it. I know this is a silly point, but you don't know how much it works.
This is all I can think of right now, sorry that this is so long. I'm willing to answer any questions if there are any.