User blog comment:CNBA3/Chapter 403 Review/Chapter 404 Prediction/@comment-7418318-20141006113950/@comment-7418318-20141006123236

But it's still worth a try I think.

If it works it works, if not, she wasted a lot of magic power that she can't properly apply anyway, so not much of a loss.

The way she is now might enable her to land a surprise hit, but I doubt she's able to put up a real fight and the chance of Erza winning this battle fast enough to stop Face are negligible, so she doesn't have anything to lose.