ATK, this is what I have prepared
Probably the silliest build I have with 12% + 12% + 12% + 12% from the set bonuses
She really doesn't need SPD, because she's going to spend most of her time in her Concerto state.
If you put ATK boots on her, she'll probably do 30-40k per hit.
And honestly, with her LC, you can probably get away with an ATK rope, too.