Short hopped reverse d-air could be pretty effective. Personally, I'd just go for a combo that guarantees you 40-50 percent... grab smash aerial kind of thing. This is also because if the Peach escapes, she can move to the situations she's strongest in, but if you hit her well above you, she'll be more vulnerable. I'm pretty sure the only effective chaingrab is the ledge chaingrab, and that can easily be extended from 0-death.
Actually, I recently figured out a way to make the ledge-chaingrab more effective. It lasts longer and is kind of easier to do, IMO. Instead of doing a dash grab, right after Nana catches them, walk forward so you're inside of the opponent's character. You only need to inch forward a tiny bit, so you can get more reps in before pushing them off the stage. If you mix tilts or blizzards in with the chaingrab, you can easily extend it to a death combo, even from 0 percent.
Also, the ledge-chaingrab is infinite on Bowser since you don't have to move to regrab him. At least, I've done it to around 300 percent on a non-DI'ing opponent, but I don't think it'll make a difference. I find it funny that the IC's have more than one grab infinite.
