Moonbow or Draconic Aura for Tana

I have just pulled 2 Tana and will be building the L&D3 Firewsweep set with the +HP, -Res copy (The other is -ATK) After the merge im not sure what exactly her attack stat will be, but At least 54. So with it being that high I will get 16 damage from DA. Should I go for it or stick with Moonbow?