Fae: Light breath+ or Dark Breath+, which to buff in weapon refinery?

So as you can see from the image I got -hp +atk Fae with Dark Breath+. I was planning to use her as a tanky debuffer who can deal with Reinhardts and Brave Lyndis. But now we are able to use weapon refinery which now makes Light Breath+ more useful than before.

However Dark Breath is still really good in its own for giving juicy debuffs for enemies and also damaging them. If I decide to use Dark Breath+ I can change atk smoke 3 seal for something more useful ( since atk smoke seal and dark breath+ debuffs won't stack eachother) something atk ploy 3, Defile Missile etc for example.

Whatever I decide to use from these 2 breaths I also need to choose what skill I should buff too. +5 hp is guranteed in every choice but which stat I should buff from these: def, res, spd or atk? Against Brave Lyn, def would be very useful since Fae has poor def already without Steady Breath A-skill. Buffing Res would help giving more use for ploy skills in seal slot + tanking other mages (I'm pretty sure it isn't enough to Deidara's or Julia's divine Naga tho). Buffing spd and atk seems to be less useful choices since they won't give enough buff to be relevant.

Any suggestions for helping my chicken to be a real monster?