This needs some more testing, but it seems (key word being "seems") that if you downB in a spot where you'd land on a drop-thru platform, you instead fall through with downB
so for example, Battlefield, Delfino, Yoshi's Island
Again, this may be specific to just 1-2 of those stages, or just happen due to the height of the ledges being just over her jump height or something, but it's something I think is worth pointing out to try some more. If it does work like it seems to from my minimal and mostly accidental use, you can attack someone standing under the ledges in a rather unique and unexpected way with this.
Another possibility: if you apply some pressure by jumping out to meet a recovering opponent, forcing them to use an upB or jump early, typically a downB back toward the stage will land you right on top of their head and able to hit.
And I've gotten in the habit of using the downB as an escape move fairly often too, due to the invincibility frames built into it. Occasionally this can line you up for a hit against more aggressive opponents.