Hi Zelda mains ! I'm probably a bit late to speak about
VS
but I can say somethings about that matchup.
Actually, Luigi can have some troubles against Zelda when it comes to grab her, the best thing to do it's to keep him away with your special attacks. Neutral B is effective when Luigi wants to approach with his fireballs, Down B and Side B can also edgeguard him. If Luigi tries to grab you but miss, you can punish him with a forward or a back air.
Luigis fears Zelda's Up Air, because you can K-O him easely due to his floaty physic.
If you are grabbed by Luigi, the best thing to do it's to try to place a Neutral Air, it can interrupt Luigi's combos, this is probably the only riposte that Zelda can do because her others attacks are hard to place.
Otherwise, you can try to double jump, Zelda is not a fast-faller so she can escape easely. Some Luigis have some troubles to combos floaty characters and forget about Up Air.
I think at the moment Zelda is not grabbed by Luigi, she will have no problem to win the fight.
P.S. : I'm actually searching a Zelda main who research a Luigi main as me to experiment team battles. If Zelda is often seen as the worst character, I think she is really good in team matches. Maybe because the Glass Canon style really fits with my playstyle or simply with Luigis. Contact me if you are interested. =)