Nowi special

Eh, I don't have Aether on my Nowi (Don't feel like foddering off B!Lucina, or paying 20k feathers on Chrom) so I just gave her Glimmer. I also gave her Sol, but that was for Tempest Trials.

It's probably best to replace Aether with something else if you don't have a reliable way to decrease the charge time. I would say Heavy Blade, but her attack isn't necessarily the highest, or at least mine isn't. My unmerged Nowi only has 48 attack with a Spd-refined Lightning Breath, and Fury 2 (she's +spd) so Heavy Blade is kinda... a waste in my opinion. But try whatever works.

Unless you are going for the arena score, replace Aether because it will never proc in time.

Glimmer

Yes in general. You should consider Bonfire instead.

But in what context are you running Nowi? How many merges?