So, you just used your second jump and I glide tossed a turnip at you accurately. Now I'm on the ledge, and the turnip is flying at you. What do you do?
1) You get hit. You don't make it to the ledge, and have to up-B.
2) You attack, catching the turnip.
3) You airdodge, missing the turnip.
4) You airdodge, catching the turnip.
Firstly, the airdodges might cause you to miss the ledge itself, forcing you to up-B just like in scenario 1. Assuming they don't, though, and that the Peach player is skilled- as you come out of the airdodge (or are in the lag from your attack), in scenario's 2, 3, and 4, you will get hit by a Peach fair and die, or possibly by nair or bair depending on a number of factors. Regardless, you won't make it back to the stage.
Option 1 gives the Peach a good shot at edgehogging you.
FYI- Peach is the best edgehogger in the game, due to the ability she has of being able to float against the ledge and release when she wants to grab, gaining invulnerability frames precisely when she wants them. Granted, that's unnecessary for Lucario's up-B, but if Lucario's trying to throw an aura sphere at you or tip you with a uair as he's falling, you can release and get the invulnerability frames, and then just hold the ledge.