Awful. She has one use and one use only - back-up Hime because of her +100 burst. So even if you lose somebody just as you're about to Full Burst, you still can blast away.
Well, I guess there is that meme use against high level Demons. Since Justitia gains Fortitude on Burst, it is possible to go infinite with her. Have Fortitude, get punched for like 50k damage, gain 100 Burst, gain Fortitude from it, get punched again for a full Burst bar... but really, that is a meme and not useful. Any Union that is able to reach high enough level against those things does NOT need to slowly grind their way through Demons with 1 Hime per turn.
tl;dr; Justitia, better than a SR, I guess!