User blog comment:Fistful of Force/DFG and Eve nerf numbers/@comment-134.50.132.170-20130116173403/@comment-24.2.35.74-20130116190744

Ult and DFG are  both based on current health, so without looking at the damage amp, it doesn't matter which order you cast them in.

With the damage amp, though, DFG will make her ult do a greater percent of the enemy's health. Therefore DFG should be cast first (Only from a pure damage standpoint. Like the op said, her ult has utility beyond damage, so there may be other reasons to use it first.)