New player - how do I deal with Zetterburn?

Hey yall

New player here, I used to play SSBU a few years back but that's my only fighting game and haven't played that in a few years. Having lots of fun with the demo, mostly playing Ranno as it feels comfortable and similar to Sheik who I played quite a lot in ultimate.

Two characters I feel frustrated playing against are Clairen and Zetterburn. Clairen just feels like I'm getting out spaced and that's fine really, I just need to play better. Zetterburn however feels horrible to play vs, maybe I'm missing something but it feels impossible to punish most of their moves and they just button mash with no lag. Frustrating to play vs because I don't know how to punish anything. Even their strong attacks are really low lag, feels like they're either attacking on in shield with hardly any downtime. Also they have a kill throw, for some reason? Or is my DI really that bad? Any suggestions?