Quote Originally Posted by thegreatonemal View Post
You're trying to blend game play elements with the lore and they don't always mix in this case they probably don't. The device throws off her echo and when the effects wear off it reactivates. The cast bar is just a gameplay thing telling you to hit her again with the thing.
In this case they likely do, because it's Stormblood, and they were pretty big on mixing what's actually going on into the gameplay of the instanced battles.