What’s the best Lightning Breath+ upgrade for Nowi?

I was considering using +speed and possibly a speed+3 seal to take her up to 36 speed (I think) if that helps, though res and defence adds to her tanking potential. I find Nowi difficult because she’s so balanced that non of her stats really shine.

I went with the +ATK Lightning Breath and haven't regretted it but since yours is +ATK you might not need the extra damage. The +RES one might be your best bet since it'll be able to patch up that RES and bring it up to a respectable number.

I wouldn't recommend going for the +SPD one. Nowi will never be super fast and you don't really want her to be anyway. She's a tank that soaks up damage and then blows her opponent away with QR + special of choice. Extra speed won't help her at all imo.

I'd recommend the +RES or +ATK one.