What's a better caeda, +atk -res or +spd -hp?

+Spd, -HP.

She has enough Res to plot units, which is why you don't want to lower it. You'll eventually want a +Atk/Spd, -Def one and merge your current one into that one.

I think +atk -hp is ideal. -res hurts her ploying ability, so maybe +spd is slightly better.