Peach's fair is +4 on shield! Fair jab is literally a block string. Against Peach, as any character, you never want to shield her float-canceled aerials. Other than dair, they are all +3 or +4. They can d-smash well before even your shine OOS comes out - in fact, she can grab before you can put any hit boxes out at all (as in you have to roll or spot dodge). If peach is floating above your lasers, you can use movement and eventually run under her. Center stage is super important for you in the matchup because you need room to evade the float canceled aerials without shielding.
Peach can actually be edge guarded fairly easily. Random invincible dairs and sudden DJ bairs can intercept her recovery from safe positions. If she gets to the ledge, she actually has almost no options to get back on stage nicely. You can abuse this by using f-throw to keep her off stage as well.